81775531 has 4 divisors (see below), whose sum is σ = 81805464. Its totient is φ = 81745600.

The previous prime is 81775517. The next prime is 81775537. The reversal of 81775531 is 13557718.

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 81775531 - 2⁹ = 81775019 is a prime.

It is a super-2 number, since 2×81775531² = 13374474940663922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81775537) 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, 10405 + ... + 16486.

It is an arithmetic number, because the mean of its divisors is an integer number (20451366).

Almost surely, 2^81775531 is an apocalyptic number.

81775531 is a deficient number, since it is larger than the sum of its proper divisors (29933).

81775531 is a wasteful number, since it uses less digits than its factorization.

81775531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29932.

The product of its digits is 29400, while the sum is 37.

The square root of 81775531 is about 9042.9824173223. The cubic root of 81775531 is about 434.0513629598.

The spelling of 81775531 in words is "eighty-one million, seven hundred seventy-five thousand, five hundred thirty-one".