81787331021 has 16 divisors (see below), whose sum is σ = 90015249408. Its totient is φ = 73694026800.

The previous prime is 81787330943. The next prime is 81787331023. The reversal of 81787331021 is 12013378718.

It is a cyclic number.

It is not a de Polignac number, because 81787331021 - 2²² = 81783136717 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81787331021.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81787331023) 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 in 15 ways as a sum of consecutive naturals, for example, 595886 + ... + 720176.

It is an arithmetic number, because the mean of its divisors is an integer number (5625953088).

Almost surely, 2^81787331021 is an apocalyptic number.

It is an amenable number.

81787331021 is a deficient number, since it is larger than the sum of its proper divisors (8227918387).

81787331021 is a wasteful number, since it uses less digits than its factorization.

81787331021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 124832.

The product of its (nonzero) digits is 56448, while the sum is 41.

The spelling of 81787331021 in words is "eighty-one billion, seven hundred eighty-seven million, three hundred thirty-one thousand, twenty-one".