31139921 has 4 divisors (see below), whose sum is σ = 31172772. Its totient is φ = 31107072.

The previous prime is 31139893. The next prime is 31139929. The reversal of 31139921 is 12993113.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12993113 = 7 ⋅1856159.

It can be written as a sum of positive squares in 2 ways, for example, as 19140625 + 11999296 = 4375^2 + 3464^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-31139921 is a prime.

It is a super-3 number, since 3×31139921³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (31139929) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 14960 + ... + 16913.

It is an arithmetic number, because the mean of its divisors is an integer number (7793193).

Almost surely, 2^31139921 is an apocalyptic number.

It is an amenable number.

31139921 is a deficient number, since it is larger than the sum of its proper divisors (32851).

31139921 is an equidigital number, since it uses as much as digits as its factorization.

31139921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32850.

The product of its digits is 1458, while the sum is 29.

The square root of 31139921 is about 5580.3154928731. The cubic root of 31139921 is about 314.6099850973.

The spelling of 31139921 in words is "thirty-one million, one hundred thirty-nine thousand, nine hundred twenty-one".