78565021 has 2 divisors, whose sum is σ = 78565022. Its totient is φ = 78565020.

The previous prime is 78565013. The next prime is 78565051. The reversal of 78565021 is 12056587.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 50623225 + 27941796 = 7115^2 + 5286^2 .

It is a cyclic number.

It is not a de Polignac number, because 78565021 - 2³ = 78565013 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78565051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39282510 + 39282511.

It is an arithmetic number, because the mean of its divisors is an integer number (39282511).

Almost surely, 2^78565021 is an apocalyptic number.

It is an amenable number.

78565021 is a deficient number, since it is larger than the sum of its proper divisors (1).

78565021 is an equidigital number, since it uses as much as digits as its factorization.

78565021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 16800, while the sum is 34.

The square root of 78565021 is about 8863.6911611360. The cubic root of 78565021 is about 428.2950715855.

The spelling of 78565021 in words is "seventy-eight million, five hundred sixty-five thousand, twenty-one".