81331651 has 2 divisors, whose sum is σ = 81331652. Its totient is φ = 81331650.

The previous prime is 81331639. The next prime is 81331669. The reversal of 81331651 is 15613318.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81331651 - 2¹⁵ = 81298883 is a prime.

It is a super-2 number, since 2×81331651² = 13229674908771602, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81331681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40665825 + 40665826.

It is an arithmetic number, because the mean of its divisors is an integer number (40665826).

Almost surely, 2^81331651 is an apocalyptic number.

81331651 is a deficient number, since it is larger than the sum of its proper divisors (1).

81331651 is an equidigital number, since it uses as much as digits as its factorization.

81331651 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2160, while the sum is 28.

The square root of 81331651 is about 9018.4062339196. The cubic root of 81331651 is about 433.2645898184.

Adding to 81331651 its reverse (15613318), we get a palindrome (96944969).

The spelling of 81331651 in words is "eighty-one million, three hundred thirty-one thousand, six hundred fifty-one".