A giant Mega Millions jackpot grew larger Wednesday to an estimated $640 million after another drawing without a winner.

No one won the lottery game’s top prize Tuesday night, making it 21 straight drawings without anyone matching all six numbers. The next drawing will be Friday night.

The huge jackpot comes less than two months after the largest lottery prize ever, a $2.04 billion Powerball prize that was won Nov. 8 in California. So far, that big winner hasn’t stepped forward to claim the prize.

The reason for all the big prizes is simple — long odds ensure there are few winners and the long streaks of lottery futility allow jackpots to grow ever larger week after week.

The odds of winning a Mega Millions jackpot is one in 302.6 million.

The advertised jackpot of $640 million is for a winner who opts to be paid with an annuity, doled out through annual payments over 29 years. Nearly all winners take the cash option, with for Friday’s drawing will be an estimated $328.3 million.

Mega Millions is played in 45 states as well as Washington, D.C., and the U.S. Virgin Islands.