81631405 has 4 divisors (see below), whose sum is σ = 97957692. Its totient is φ = 65305120.

The previous prime is 81631379. The next prime is 81631421. The reversal of 81631405 is 50413618.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 57562569 + 24068836 = 7587^2 + 4906^2 .

It is not a de Polignac number, because 81631405 - 2⁵ = 81631373 is a prime.

It is a Duffinian number.

It is a congruent 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, 8163136 + ... + 8163145.

It is an arithmetic number, because the mean of its divisors is an integer number (24489423).

Almost surely, 2^81631405 is an apocalyptic number.

It is an amenable number.

81631405 is a deficient number, since it is larger than the sum of its proper divisors (16326287).

81631405 is a wasteful number, since it uses less digits than its factorization.

81631405 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16326286.

The product of its (nonzero) digits is 2880, while the sum is 28.

The square root of 81631405 is about 9035.0099612563. The cubic root of 81631405 is about 433.7962137972.

The spelling of 81631405 in words is "eighty-one million, six hundred thirty-one thousand, four hundred five".