81956809 has 9 divisors (see below), whose sum is σ = 90194349. Its totient is φ = 74415660.

The previous prime is 81956803. The next prime is 81956851. The reversal of 81956809 is 90865918.

The square root of 81956809 is 9053.

It is a perfect power (a square), and thus also a powerful number.

It is a de Polignac number, because none of the positive numbers 2^k-81956809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81956803) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 99172 + ... + 99994.

Almost surely, 2^81956809 is an apocalyptic number.

81956809 is the 9053-rd square number.

81956809 is the 4527-th centered octagonal number.

It is an amenable number.

81956809 is a deficient number, since it is larger than the sum of its proper divisors (8237540).

81956809 is an frugal number, since it uses more digits than its factorization.

81956809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1668 (or 834 counting only the distinct ones).

The product of its (nonzero) digits is 155520, while the sum is 46.

The cubic root of 81956809 is about 434.3718577417.

It can be divided in two parts, 8195 and 6809, that multiplied together give a palindrome (55799755).

The spelling of 81956809 in words is "eighty-one million, nine hundred fifty-six thousand, eight hundred nine".