391779964889921 has 2 divisors, whose sum is σ = 391779964889922. Its totient is φ = 391779964889920.

The previous prime is 391779964889821. The next prime is 391779964889947. The reversal of 391779964889921 is 129988469977193.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 204370326514225 + 187409638375696 = 14295815^2 + 13689764^2 .

It is a cyclic number.

It is not a de Polignac number, because 391779964889921 - 2¹⁴ = 391779964873537 is a prime.

It is a super-4 number, since 4×391779964889921⁴ (a number of 59 digits) contains 4444 as substring.

It is not a weakly prime, because it can be changed into another prime (391779964889981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195889982444960 + 195889982444961.

It is an arithmetic number, because the mean of its divisors is an integer number (195889982444961).

Almost surely, 2^{391779964889921} is an apocalyptic number.

It is an amenable number.

391779964889921 is a deficient number, since it is larger than the sum of its proper divisors (1).

391779964889921 is an equidigital number, since it uses as much as digits as its factorization.

391779964889921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 26665583616, while the sum is 92.

The spelling of 391779964889921 in words is "three hundred ninety-one trillion, seven hundred seventy-nine billion, nine hundred sixty-four million, eight hundred eighty-nine thousand, nine hundred twenty-one".