81557531 has 4 divisors (see below), whose sum is σ = 88971864. Its totient is φ = 74143200.

The previous prime is 81557479. The next prime is 81557537. The reversal of 81557531 is 13575518.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81557531 - 2¹⁸ = 81295387 is a prime.

It is a super-2 number, since 2×81557531² = 13303261725631922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81557491 and 81557500.

It is not an unprimeable number, because it can be changed into a prime (81557537) 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, 3707150 + ... + 3707171.

It is an arithmetic number, because the mean of its divisors is an integer number (22242966).

Almost surely, 2^81557531 is an apocalyptic number.

81557531 is a deficient number, since it is larger than the sum of its proper divisors (7414333).

81557531 is a wasteful number, since it uses less digits than its factorization.

81557531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7414332.

The product of its digits is 21000, while the sum is 35.

The square root of 81557531 is about 9030.9208279112. The cubic root of 81557531 is about 433.6653167348.

The spelling of 81557531 in words is "eighty-one million, five hundred fifty-seven thousand, five hundred thirty-one".