81637281 has 128 divisors (see below), whose sum is σ = 157593600. Its totient is φ = 41057280.

The previous prime is 81637279. The next prime is 81637313. The reversal of 81637281 is 18273618.

It is not a de Polignac number, because 81637281 - 2¹ = 81637279 is a prime.

It is a super-2 number, since 2×81637281² = 13329291298145922, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81637201) by changing a digit.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 2206395 + ... + 2206431.

It is an arithmetic number, because the mean of its divisors is an integer number (1231200).

Almost surely, 2^81637281 is an apocalyptic number.

It is an amenable number.

81637281 is a deficient number, since it is larger than the sum of its proper divisors (75956319).

81637281 is a wasteful number, since it uses less digits than its factorization.

81637281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 116 (or 110 counting only the distinct ones).

The product of its digits is 16128, while the sum is 36.

The square root of 81637281 is about 9035.3351349023. The cubic root of 81637281 is about 433.8066220683.

It can be divided in two parts, 81637 and 281, that added together give a palindrome (81918).

The spelling of 81637281 in words is "eighty-one million, six hundred thirty-seven thousand, two hundred eighty-one".