81779531 has 4 divisors (see below), whose sum is σ = 81884232. Its totient is φ = 81674832.

The previous prime is 81779527. The next prime is 81779561. The reversal of 81779531 is 13597718.

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 81779531 - 2² = 81779527 is a prime.

It is a super-2 number, since 2×81779531² = 13375783381159922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81779521) 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, 51170 + ... + 52743.

It is an arithmetic number, because the mean of its divisors is an integer number (20471058).

Almost surely, 2^81779531 is an apocalyptic number.

81779531 is a deficient number, since it is larger than the sum of its proper divisors (104701).

81779531 is a wasteful number, since it uses less digits than its factorization.

81779531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 104700.

The product of its digits is 52920, while the sum is 41.

The square root of 81779531 is about 9043.2035805902. The cubic root of 81779531 is about 434.0584399633.

The spelling of 81779531 in words is "eighty-one million, seven hundred seventy-nine thousand, five hundred thirty-one".