81609631 has 2 divisors, whose sum is σ = 81609632. Its totient is φ = 81609630.

The previous prime is 81609629. The next prime is 81609641. The reversal of 81609631 is 13690618.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81609631 - 2¹ = 81609629 is a prime.

It is a super-2 number, since 2×81609631² = 13320263743912322, which contains 22 as substring.

Together with 81609629, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81609641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40804815 + 40804816.

It is an arithmetic number, because the mean of its divisors is an integer number (40804816).

Almost surely, 2^81609631 is an apocalyptic number.

81609631 is a deficient number, since it is larger than the sum of its proper divisors (1).

81609631 is an equidigital number, since it uses as much as digits as its factorization.

81609631 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7776, while the sum is 34.

The square root of 81609631 is about 9033.8049015905. The cubic root of 81609631 is about 433.7576407394.

The spelling of 81609631 in words is "eighty-one million, six hundred nine thousand, six hundred thirty-one".