81900081 has 6 divisors (see below), whose sum is σ = 118300130. Its totient is φ = 54600048.

The previous prime is 81900061. The next prime is 81900097. The reversal of 81900081 is 18000918.

It can be written as a sum of positive squares in only one way, i.e., 73256481 + 8643600 = 8559^2 + 2940^2 .

It is not a de Polignac number, because 81900081 - 2⁶ = 81900017 is a prime.

It is a super-2 number, since 2×81900081² = 13415246535613122, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81900061) 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, 4549996 + ... + 4550013.

Almost surely, 2^81900081 is an apocalyptic number.

It is an amenable number.

81900081 is a deficient number, since it is larger than the sum of its proper divisors (36400049).

81900081 is a wasteful number, since it uses less digits than its factorization.

81900081 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9100015 (or 9100012 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 27.

The square root of 81900081 is about 9049.8663526043. The cubic root of 81900081 is about 434.2716149655.

Adding to 81900081 its reverse (18000918), we get a palindrome (99900999).

The spelling of 81900081 in words is "eighty-one million, nine hundred thousand, eighty-one".