81560372921 has 2 divisors, whose sum is σ = 81560372922. Its totient is φ = 81560372920.

The previous prime is 81560372917. The next prime is 81560372941. The reversal of 81560372921 is 12927306518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 76292516521 + 5267856400 = 276211^2 + 72580^2 .

It is a cyclic number.

It is not a de Polignac number, because 81560372921 - 2² = 81560372917 is a prime.

It is not a weakly prime, because it can be changed into another prime (81560372941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40780186460 + 40780186461.

It is an arithmetic number, because the mean of its divisors is an integer number (40780186461).

Almost surely, 2^81560372921 is an apocalyptic number.

It is an amenable number.

81560372921 is a deficient number, since it is larger than the sum of its proper divisors (1).

81560372921 is an equidigital number, since it uses as much as digits as its factorization.

81560372921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 181440, while the sum is 44.

The spelling of 81560372921 in words is "eighty-one billion, five hundred sixty million, three hundred seventy-two thousand, nine hundred twenty-one".