21261231 has 16 divisors (see below), whose sum is σ = 31697920. Its totient is φ = 14084280.

The previous prime is 21261217. The next prime is 21261239. The reversal of 21261231 is 13216212.

21261231 is a `hidden beast` number, since 21 + 2 + 612 + 31 = 666.

It is not a de Polignac number, because 21261231 - 2⁷ = 21261103 is a prime.

It is a super-2 number, since 2×21261231² = 904079887270722, 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 (21261239) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1986 + ... + 6816.

It is an arithmetic number, because the mean of its divisors is an integer number (1981120).

Almost surely, 2^21261231 is an apocalyptic number.

21261231 is a deficient number, since it is larger than the sum of its proper divisors (10436689).

21261231 is a wasteful number, since it uses less digits than its factorization.

21261231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5003 (or 4997 counting only the distinct ones).

The product of its digits is 144, while the sum is 18.

The square root of 21261231 is about 4610.9902407184. The cubic root of 21261231 is about 277.0317010294.

Adding to 21261231 its reverse (13216212), we get a palindrome (34477443).

The spelling of 21261231 in words is "twenty-one million, two hundred sixty-one thousand, two hundred thirty-one".