77990921 has 8 divisors (see below), whose sum is σ = 78942600. Its totient is φ = 77045248.

The previous prime is 77990911. The next prime is 77990929. The reversal of 77990921 is 12909977.

It can be written as a sum of positive squares in 4 ways, for example, as 22934521 + 55056400 = 4789^2 + 7420^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-77990921 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (77990929) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 28025 + ... + 30681.

It is an arithmetic number, because the mean of its divisors is an integer number (9867825).

Almost surely, 2^77990921 is an apocalyptic number.

77990921 is the 4721-st centered heptagonal number.

It is an amenable number.

77990921 is a deficient number, since it is larger than the sum of its proper divisors (951679).

77990921 is a wasteful number, since it uses less digits than its factorization.

77990921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3003.

The product of its (nonzero) digits is 71442, while the sum is 44.

The square root of 77990921 is about 8831.2468542103. The cubic root of 77990921 is about 427.2492899761.

The spelling of 77990921 in words is "seventy-seven million, nine hundred ninety thousand, nine hundred twenty-one".