81994508639 has 2 divisors, whose sum is σ = 81994508640. Its totient is φ = 81994508638.

The previous prime is 81994508597. The next prime is 81994508663. The reversal of 81994508639 is 93680549918.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81994508639 - 2⁸ = 81994508383 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81994508839) 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, 40997254319 + 40997254320.

It is an arithmetic number, because the mean of its divisors is an integer number (40997254320).

Almost surely, 2^81994508639 is an apocalyptic number.

81994508639 is a deficient number, since it is larger than the sum of its proper divisors (1).

81994508639 is an equidigital number, since it uses as much as digits as its factorization.

81994508639 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 16796160, while the sum is 62.

The spelling of 81994508639 in words is "eighty-one billion, nine hundred ninety-four million, five hundred eight thousand, six hundred thirty-nine".