81921231 has 24 divisors (see below), whose sum is σ = 137458464. Its totient is φ = 46042560.

The previous prime is 81921227. The next prime is 81921241. The reversal of 81921231 is 13212918.

It is not a de Polignac number, because 81921231 - 2² = 81921227 is a prime.

It is a super-2 number, since 2×81921231² = 13422176177110722, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 81921195 and 81921204.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81921211) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6816 + ... + 14501.

It is an arithmetic number, because the mean of its divisors is an integer number (5727436).

Almost surely, 2^81921231 is an apocalyptic number.

81921231 is a deficient number, since it is larger than the sum of its proper divisors (55537233).

81921231 is a wasteful number, since it uses less digits than its factorization.

81921231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21391 (or 21388 counting only the distinct ones).

The product of its digits is 864, while the sum is 27.

The square root of 81921231 is about 9051.0348027173. The cubic root of 81921231 is about 434.3089940662.

The spelling of 81921231 in words is "eighty-one million, nine hundred twenty-one thousand, two hundred thirty-one".