81312137 has 4 divisors (see below), whose sum is σ = 81330756. Its totient is φ = 81293520.

The previous prime is 81312109. The next prime is 81312157. The reversal of 81312137 is 73121318.

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 14661241 + 66650896 = 3829^2 + 8164^2 .

It is a cyclic number.

It is not a de Polignac number, because 81312137 - 2¹⁸ = 81049993 is a prime.

It is a super-2 number, since 2×81312137² = 13223327247013538, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81312157) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1187 + ... + 12807.

It is an arithmetic number, because the mean of its divisors is an integer number (20332689).

Almost surely, 2^81312137 is an apocalyptic number.

It is an amenable number.

81312137 is a deficient number, since it is larger than the sum of its proper divisors (18619).

81312137 is a wasteful number, since it uses less digits than its factorization.

81312137 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18618.

The product of its digits is 1008, while the sum is 26.

The square root of 81312137 is about 9017.3242705361. The cubic root of 81312137 is about 433.2299358168.

The spelling of 81312137 in words is "eighty-one million, three hundred twelve thousand, one hundred thirty-seven".