81968639 has 2 divisors, whose sum is σ = 81968640. Its totient is φ = 81968638.

The previous prime is 81968633. The next prime is 81968651. The reversal of 81968639 is 93686918.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81968639 - 2¹² = 81964543 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81968633) 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, 40984319 + 40984320.

It is an arithmetic number, because the mean of its divisors is an integer number (40984320).

Almost surely, 2^81968639 is an apocalyptic number.

81968639 is a deficient number, since it is larger than the sum of its proper divisors (1).

81968639 is an equidigital number, since it uses as much as digits as its factorization.

81968639 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 559872, while the sum is 50.

The square root of 81968639 is about 9053.6533509959. The cubic root of 81968639 is about 434.3927564399.

The spelling of 81968639 in words is "eighty-one million, nine hundred sixty-eight thousand, six hundred thirty-nine".