81900905 has 4 divisors (see below), whose sum is σ = 98281092. Its totient is φ = 65520720.

The previous prime is 81900893. The next prime is 81900947. The reversal of 81900905 is 50900918.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 50900918 = 2 ⋅25450459.

It can be written as a sum of positive squares in 2 ways, for example, as 14348944 + 67551961 = 3788^2 + 8219^2 .

It is not a de Polignac number, because 81900905 - 2¹⁴ = 81884521 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8190086 + ... + 8190095.

It is an arithmetic number, because the mean of its divisors is an integer number (24570273).

Almost surely, 2^81900905 is an apocalyptic number.

It is an amenable number.

81900905 is a deficient number, since it is larger than the sum of its proper divisors (16380187).

81900905 is a wasteful number, since it uses less digits than its factorization.

81900905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16380186.

The product of its (nonzero) digits is 3240, while the sum is 32.

The square root of 81900905 is about 9049.9118780240. The cubic root of 81900905 is about 434.2730713686.

The spelling of 81900905 in words is "eighty-one million, nine hundred thousand, nine hundred five".