21131231 has 4 divisors (see below), whose sum is σ = 23052264. Its totient is φ = 19210200.

The previous prime is 21131191. The next prime is 21131251. The reversal of 21131231 is 13213112.

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-21131231 is a prime.

It is a super-2 number, since 2×21131231² = 893057847150722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21131251) 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, 960500 + ... + 960521.

It is an arithmetic number, because the mean of its divisors is an integer number (5763066).

Almost surely, 2^21131231 is an apocalyptic number.

21131231 is a deficient number, since it is larger than the sum of its proper divisors (1921033).

21131231 is a wasteful number, since it uses less digits than its factorization.

21131231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1921032.

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

The square root of 21131231 is about 4596.8718711750. The cubic root of 21131231 is about 276.4659173382.

Adding to 21131231 its reverse (13213112), we get a palindrome (34344343).

The spelling of 21131231 in words is "twenty-one million, one hundred thirty-one thousand, two hundred thirty-one".