31218813 has 12 divisors (see below), whose sum is σ = 45366048. Its totient is φ = 20686920.

The previous prime is 31218809. The next prime is 31218823. The reversal of 31218813 is 31881213.

It is not a de Polignac number, because 31218813 - 2² = 31218809 is a prime.

It is a super-2 number, since 2×31218813² = 1949228570257938, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31218823) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 8883 + ... + 11888.

It is an arithmetic number, because the mean of its divisors is an integer number (3780504).

Almost surely, 2^31218813 is an apocalyptic number.

It is an amenable number.

31218813 is a deficient number, since it is larger than the sum of its proper divisors (14147235).

31218813 is a wasteful number, since it uses less digits than its factorization.

31218813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20944 (or 20941 counting only the distinct ones).

The product of its digits is 1152, while the sum is 27.

The square root of 31218813 is about 5587.3797973648. The cubic root of 31218813 is about 314.8754458435.

It can be divided in two parts, 3 and 1218813, that added together give a square (1218816 = 1104²).

The spelling of 31218813 in words is "thirty-one million, two hundred eighteen thousand, eight hundred thirteen".