77989921 has 2 divisors, whose sum is σ = 77989922. Its totient is φ = 77989920.

The previous prime is 77989909. The next prime is 77989937. The reversal of 77989921 is 12998977.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 69222400 + 8767521 = 8320^2 + 2961^2 .

It is an emirp because it is prime and its reverse (12998977) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-77989921 is a prime.

It is not a weakly prime, because it can be changed into another prime (77989621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 38994960 + 38994961.

It is an arithmetic number, because the mean of its divisors is an integer number (38994961).

Almost surely, 2^77989921 is an apocalyptic number.

It is an amenable number.

77989921 is a deficient number, since it is larger than the sum of its proper divisors (1).

77989921 is an equidigital number, since it uses as much as digits as its factorization.

77989921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 571536, while the sum is 52.

The square root of 77989921 is about 8831.1902368820. The cubic root of 77989921 is about 427.2474639040.

The spelling of 77989921 in words is "seventy-seven million, nine hundred eighty-nine thousand, nine hundred twenty-one".