81511631 has 2 divisors, whose sum is σ = 81511632. Its totient is φ = 81511630.

The previous prime is 81511607. The next prime is 81511669. The reversal of 81511631 is 13611518.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81511631 - 2¹⁴ = 81495247 is a prime.

It is a super-2 number, since 2×81511631² = 13288291976560322, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81511631.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81511681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40755815 + 40755816.

It is an arithmetic number, because the mean of its divisors is an integer number (40755816).

Almost surely, 2^81511631 is an apocalyptic number.

81511631 is a deficient number, since it is larger than the sum of its proper divisors (1).

81511631 is an equidigital number, since it uses as much as digits as its factorization.

81511631 is an evil number, because the sum of its binary digits is even.

The product of its digits is 720, while the sum is 26.

The square root of 81511631 is about 9028.3792011634. The cubic root of 81511631 is about 433.5839468800.

The spelling of 81511631 in words is "eighty-one million, five hundred eleven thousand, six hundred thirty-one".