March Madness is heading to the Sweet 16 without a handful of top teams. Two No. 1 seeds, Kansas and Purdue, No. 2 seed Arizona and No. 4 seed Virginia are all gone - and gone with them are millions of busted brackets.

It's been tough sledding for the bluebloods, too: Besides Kansas, Kentucky, Duke and Indiana are all heading home. UCLA's drive for a 12th national title remains alive.

Here is what to know with the regional semifinals up next at the NCAA Tournament:

The top four seeds in the tournament were given to Alabama, Houston, Kansas and Purdue. Each had its share of headaches to set up what is proving to be a chaotic tournament. The Boilermakers were the first to fall, ousted in a first-round stunner, and the Jayhawks followed the very next day.

EAST REGION: The Boilermakers got a top seed for the fourth time, but Purdue was dumped by Fairleigh Dickinson in a near-historic upset. and the 2-seed, Marquette, is also gone. Up next: No. 9 seed FAU vs. No. 4 seed Tennessee and No. 3 seed Kansas State vs. No. 7 seed Michigan State, whose coach Tom Izzo is heading to his 15th regional.

SOUTH REGION: Alabama, led by coach Nate Oats in a challenging season, got a top seed for the first time behind SEC player of the year Brandon Miller, who has armed security on hand after being the subject of threats. Up next: No. 1 seed Alabama vs. No. 5 seed San Diego State and No. 6 seed Creighton vs. No. 15 seed Princeton, which is in rare territory.

MIDWEST REGION: Houston got a top seed and won its opener before a rugged victory over Auburn even with All-American Marcus Sasser hobbled by a groin injury. Up next: No. 1 seed Houston vs. No. 5 seed Miami and No. 2 seed Texas vs. No. 3 seed Xavier.

WEST REGION: Kansas, the top-seeded defending national champion that was without coach Bill Self in the tournament following a heart procedure, blew an 8-point halftime lead and lost to Arkansas. Up next: No. 2 seed UCLA vs. No. 3 Gonzaga and No. 4 seed UConn vs. No. 8 seed Arkansas.

The unforgettable plays are piling up.

Princeton used a late run to earn its first NCAA Tournament win in 25 years by ousting No. 2 seed Arizona and then answered any skeptics by rolling Missouri to lock in its first Sweet 16 spot in 56 years.

Furman celebrated its first tourney appearance since 1980 with a win over No. 4 seed Virginia on a deep 3-pointer by JP Pegues with 2.4 seconds left. Then came 16-seed Fairleigh Dickinson's win over Purdue as the 22 1/2-point underdog stifled 7-4 center Zach Edey to advance and join UMBC in the record books.

All that happened before the Razorbacks and shirtless coach Eric Musselman celebrated their win over the Jayhawks.

No. 4 seed Connecticut (27-8) vs. No. 8 seed Arkansas (22-13), Thursday, 7:15 p.m. ET (CBS)

The Huskies are returning to the Sweet 16 for the first time in nine years, and hoping to avoid being the next victim of Arkansas, which ousted defending champion Kansas. UConn outclassed Saint Mary’s 70-55 behind 24 points by Adama Sanogo and timely 3-point shooting.

No. 2 Kansas State (25-9) vs. No. 7 Michigan State (21-12), Thursday, 6:30 p.m. ET (TBS)

Tom Izzo is taking Michigan State to the Sweet 16 for the 15th time and first in four years after a 69-60 victory against No. 2 seed Marquette. The victory was the 16th for Izzo in the tournament against a higher seed, breaking the record he shared with recently retired Syracuse coach Jim Boeheim. At Madison Square Garden, the Spartans will face a Kansas State team that was picked to finish last in the Big 12 with a remade roster and first-year coach in Jerome Tang. The Wildcats outlasted Kentucky 75-69 behind 27 points by Markquis Nowell.

No. 5 seed San Diego State (29-6) vs. No. 1 seed Alabama (31-5), Friday, 6:30 p.m. ET (TBS)

The Aztecs are heading to the Sweet 16 for the first time since 2004 and have won 11 of their last 13. Balanced scoring carried them to a second-round victory against Furman and they’ll need more of the same against the Crimson Tide, who handily dispatched Maryland in the second round. All-America freshman Brandon Miller, who is nursing an injury, had 19 after going scoreless in the first round.

No. 3 seed Xavier (27-9) vs. No. 2 seed Texas (28-8), Friday, 9:45 p.m. ET (CBS)

The Musketeers are heading to the Sweet 16 for the first time since 2017 and will face a Longhorns team that hasn’t been there in 15 years. Xavier put on a clinic on unselfishness in the first half of its 84-73 victory against Pittsburgh, totaling 17 assists on 19 made field goals. The Longhorns made just one 3-pointer in 13 tries in their 71-66 victory against Penn State, but Dylan Disu had season-high 28-point performance.

The SEC and Big Ten led the way by placing eight teams each in the 68-team field. Conference USA (Florida Atlantic) and the Ivy League (Princeton) each got one team into the tournament and both are still alive. The rest of the leagues can't say that. The records through two rounds:

ACC (5 teams made tourney): 5-4. One team left (Miami). American Athletic (2): 2-1. One team left (Houston). Big 12 (7): 7-5. Two teams left (Kansas State, Texas). Big East (5): 7-2. Three teams left (Creighton, UConn, Xavier). Big Ten (8): 6-7. One team left (Michigan State). Mountain West (4): 2-3. One team left (San Diego State). Pac-12 (4): 3-3. One team left (UCLA). SEC (8): 9-5. Three teams left (Alabama, Arkansas, Tennessee). West Coast (2): 3-1. One team left (Gonzaga).

Gun violence has cost lives and disrupted college sports all season, touching some of the top programs in college basketball, including Alabama. Coaches have been thrust into uncertain and unwelcome roles in trying to navigate the topic - as well as the fallout from the Supreme Court decision to overturn Roe vs. Wade.

On a lighter note, if you feel you know March Madness pretty well, try this 25-question trivia quiz put together by AP.

The NCAA Tournament is filled with great players and the AP All-America team is a good place to get familiar with the names. It's also an event where guys you've never heard of can take a star turn. Guard play is always going to be important (see: Baylor, 2021 title winner) and there are some NBA prospects in the mix.

Bet on this, too: Some player - maybe more than one - will have a chance to join the mustachioed Doug Edert (remember Saint Peters' inspiring run last year?) and find a way to cash in on their celebrity.

Every game of the men’s tournament will be aired - here is a schedule - either on CBS, TBS, TNT or TruTV and their digital platforms. CBS, which also has a handy schedule that includes announcing teams, will handle the Final Four and national title game this year.

The NCAA is streaming games via its March Madness Live option and CBS games are being streamed on Paramount+. Fans of longtime play-by-play announcer Jim Nantz should soak up every moment: It’s his final NCAA Tournament.

Who's going to win the national championship? The betting favorites to reach the Final Four are (in order, as of March 19): Alabama, Houston, UConn, UCLA, Gonzaga and Texas, according to FanDuel Sportsbook.

Sweet 16 weekend will see games in New York City (East Region), Las Vegas (West), Kansas City, Missouri (Midwest), and Louisville, Kentucky (South).

Where is the Final Four? In Houston, on April 1, with the championship game on April 3. Basketball aficionados, take note: The women’s NCAA Tournament will hold its Final Four in Dallas, a four-hour drive up the road from Houston.

Can't get enough March Madness? Well, there is talk about expanding the tournament despite a host of challenges. Enjoy the 68-team version for now!