21213131 has 4 divisors (see below), whose sum is σ = 21423264. Its totient is φ = 21003000.

The previous prime is 21213119. The next prime is 21213149. The reversal of 21213131 is 13131212.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21213131 is a prime.

It is a super-2 number, since 2×21213131² = 899993853646322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21213431) 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, 104915 + ... + 105116.

It is an arithmetic number, because the mean of its divisors is an integer number (5355816).

Almost surely, 2^21213131 is an apocalyptic number.

21213131 is a deficient number, since it is larger than the sum of its proper divisors (210133).

21213131 is a wasteful number, since it uses less digits than its factorization.

21213131 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 210132.

The product of its digits is 36, while the sum is 14.

The square root of 21213131 is about 4605.7714880354. The cubic root of 21213131 is about 276.8226305673.

Adding to 21213131 its reverse (13131212), we get a palindrome (34344343).

It can be divided in two parts, 21213 and 131, that multiplied together give a triangular number (2778903 = T₂₃₅₇).

The spelling of 21213131 in words is "twenty-one million, two hundred thirteen thousand, one hundred thirty-one".