81643631 has 4 divisors (see below), whose sum is σ = 81777432. Its totient is φ = 81509832.

The previous prime is 81643609. The next prime is 81643651. The reversal of 81643631 is 13634618.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 13634618 = 2 ⋅6817309.

It is a cyclic number.

It is not a de Polignac number, because 81643631 - 2⁶ = 81643567 is a prime.

It is a super-2 number, since 2×81643631² = 13331364965728322, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81643651) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 65981 + ... + 67206.

It is an arithmetic number, because the mean of its divisors is an integer number (20444358).

Almost surely, 2^81643631 is an apocalyptic number.

81643631 is a deficient number, since it is larger than the sum of its proper divisors (133801).

81643631 is a wasteful number, since it uses less digits than its factorization.

81643631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 133800.

The product of its digits is 10368, while the sum is 32.

The square root of 81643631 is about 9035.6865262137. The cubic root of 81643631 is about 433.8178693833.

The spelling of 81643631 in words is "eighty-one million, six hundred forty-three thousand, six hundred thirty-one".