81919631 has 4 divisors (see below), whose sum is σ = 82044600. Its totient is φ = 81794664.

The previous prime is 81919619. The next prime is 81919633. The reversal of 81919631 is 13691918.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 13691918 = 2 ⋅6845959.

It is a cyclic number.

It is not a de Polignac number, because 81919631 - 2⁶ = 81919567 is a prime.

It is a super-2 number, since 2×81919631² = 13421651886352322, 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 (81919633) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 61496 + ... + 62813.

It is an arithmetic number, because the mean of its divisors is an integer number (20511150).

Almost surely, 2^81919631 is an apocalyptic number.

81919631 is a deficient number, since it is larger than the sum of its proper divisors (124969).

81919631 is a wasteful number, since it uses less digits than its factorization.

81919631 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 124968.

The product of its digits is 11664, while the sum is 38.

The square root of 81919631 is about 9050.9464146022. The cubic root of 81919631 is about 434.3061665578.

The spelling of 81919631 in words is "eighty-one million, nine hundred nineteen thousand, six hundred thirty-one".