77915921 has 2 divisors, whose sum is σ = 77915922. Its totient is φ = 77915920.

The previous prime is 77915917. The next prime is 77915923. The reversal of 77915921 is 12951977.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 52765696 + 25150225 = 7264^2 + 5015^2 .

It is a cyclic number.

It is not a de Polignac number, because 77915921 - 2² = 77915917 is a prime.

Together with 77915923, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (77915923) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 38957960 + 38957961.

It is an arithmetic number, because the mean of its divisors is an integer number (38957961).

Almost surely, 2^77915921 is an apocalyptic number.

It is an amenable number.

77915921 is a deficient number, since it is larger than the sum of its proper divisors (1).

77915921 is an equidigital number, since it uses as much as digits as its factorization.

77915921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 39690, while the sum is 41.

The square root of 77915921 is about 8826.9995468449. Note that the first 3 decimals coincide. The cubic root of 77915921 is about 427.1122912355.

The spelling of 77915921 in words is "seventy-seven million, nine hundred fifteen thousand, nine hundred twenty-one".