78611668021 has 2 divisors, whose sum is σ = 78611668022. Its totient is φ = 78611668020.

The previous prime is 78611668019. The next prime is 78611668033. The reversal of 78611668021 is 12086611687.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 56282343121 + 22329324900 = 237239^2 + 149430^2 .

It is a cyclic number.

It is not a de Polignac number, because 78611668021 - 2¹ = 78611668019 is a prime.

Together with 78611668019, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78611668001) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39305834010 + 39305834011.

It is an arithmetic number, because the mean of its divisors is an integer number (39305834011).

Almost surely, 2^78611668021 is an apocalyptic number.

It is an amenable number.

78611668021 is a deficient number, since it is larger than the sum of its proper divisors (1).

78611668021 is an equidigital number, since it uses as much as digits as its factorization.

78611668021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 193536, while the sum is 46.

The spelling of 78611668021 in words is "seventy-eight billion, six hundred eleven million, six hundred sixty-eight thousand, twenty-one".