81537692021 has 2 divisors, whose sum is σ = 81537692022. Its totient is φ = 81537692020.

The previous prime is 81537692009. The next prime is 81537692029. The reversal of 81537692021 is 12029673518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 53886658225 + 27651033796 = 232135^2 + 166286^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81537692021 is a prime.

It is a super-2 number, since 2×81537692021² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81537692029) 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, 40768846010 + 40768846011.

It is an arithmetic number, because the mean of its divisors is an integer number (40768846011).

Almost surely, 2^81537692021 is an apocalyptic number.

It is an amenable number.

81537692021 is a deficient number, since it is larger than the sum of its proper divisors (1).

81537692021 is an equidigital number, since it uses as much as digits as its factorization.

81537692021 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 81537692021 in words is "eighty-one billion, five hundred thirty-seven million, six hundred ninety-two thousand, twenty-one".