78664021 has 2 divisors, whose sum is σ = 78664022. Its totient is φ = 78664020.

The previous prime is 78663973. The next prime is 78664039. The reversal of 78664021 is 12046687.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 62583921 + 16080100 = 7911^2 + 4010^2 .

It is a cyclic number.

It is not a de Polignac number, because 78664021 - 2⁹ = 78663509 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78664121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39332010 + 39332011.

It is an arithmetic number, because the mean of its divisors is an integer number (39332011).

Almost surely, 2^78664021 is an apocalyptic number.

It is an amenable number.

78664021 is a deficient number, since it is larger than the sum of its proper divisors (1).

78664021 is an equidigital number, since it uses as much as digits as its factorization.

78664021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 16128, while the sum is 34.

The square root of 78664021 is about 8869.2739838163. The cubic root of 78664021 is about 428.4748946758.

The spelling of 78664021 in words is "seventy-eight million, six hundred sixty-four thousand, twenty-one".