81531 has 6 divisors (see below), whose sum is σ = 117780. Its totient is φ = 54348.

The previous prime is 81527. The next prime is 81533. The reversal of 81531 is 13518.

It is a happy number.

It is not a de Polignac number, because 81531 - 2² = 81527 is a prime.

It is a super-2 number, since 2×81531² = 13294607922, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81533) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4521 + ... + 4538.

It is an arithmetic number, because the mean of its divisors is an integer number (19630).

2⁸¹⁵³¹ is an apocalyptic number.

81531 is a deficient number, since it is larger than the sum of its proper divisors (36249).

81531 is a wasteful number, since it uses less digits than its factorization.

81531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9065 (or 9062 counting only the distinct ones).

The product of its digits is 120, while the sum is 18.

The square root of 81531 is about 285.5363374424. The cubic root of 81531 is about 43.3618287265.

The spelling of 81531 in words is "eighty-one thousand, five hundred thirty-one".