391647833921 has 2 divisors, whose sum is σ = 391647833922. Its totient is φ = 391647833920.

The previous prime is 391647833879. The next prime is 391647833959. The reversal of 391647833921 is 129338746193.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 391093890625 + 553943296 = 625375^2 + 23536^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-391647833921 is a prime.

It is a super-2 number, since 2×391647833921² (a number of 24 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (391647833971) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195823916960 + 195823916961.

It is an arithmetic number, because the mean of its divisors is an integer number (195823916961).

Almost surely, 2^391647833921 is an apocalyptic number.

It is an amenable number.

391647833921 is a deficient number, since it is larger than the sum of its proper divisors (1).

391647833921 is an equidigital number, since it uses as much as digits as its factorization.

391647833921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5878656, while the sum is 56.

The spelling of 391647833921 in words is "three hundred ninety-one billion, six hundred forty-seven million, eight hundred thirty-three thousand, nine hundred twenty-one".