21556231 has 2 divisors, whose sum is σ = 21556232. Its totient is φ = 21556230.

The previous prime is 21556211. The next prime is 21556247. The reversal of 21556231 is 13265512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21556231 - 2⁷ = 21556103 is a prime.

It is a super-2 number, since 2×21556231² = 929342189850722, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21556196 and 21556205.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21556211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778115 + 10778116.

It is an arithmetic number, because the mean of its divisors is an integer number (10778116).

Almost surely, 2^21556231 is an apocalyptic number.

21556231 is a deficient number, since it is larger than the sum of its proper divisors (1).

21556231 is an equidigital number, since it uses as much as digits as its factorization.

21556231 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1800, while the sum is 25.

The square root of 21556231 is about 4642.8688329523. The cubic root of 21556231 is about 278.3070938328.

The spelling of 21556231 in words is "twenty-one million, five hundred fifty-six thousand, two hundred thirty-one".