21555931 has 2 divisors, whose sum is σ = 21555932. Its totient is φ = 21555930.

The previous prime is 21555923. The next prime is 21555967. The reversal of 21555931 is 13955512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21555931 - 2³ = 21555923 is a prime.

It is a super-2 number, since 2×21555931² = 929316322553522, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21555893 and 21555902.

It is not a weakly prime, because it can be changed into another prime (21535931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10777965 + 10777966.

It is an arithmetic number, because the mean of its divisors is an integer number (10777966).

Almost surely, 2^21555931 is an apocalyptic number.

21555931 is a deficient number, since it is larger than the sum of its proper divisors (1).

21555931 is an equidigital number, since it uses as much as digits as its factorization.

21555931 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6750, while the sum is 31.

The square root of 21555931 is about 4642.8365252289. The cubic root of 21555931 is about 278.3058027519.

The spelling of 21555931 in words is "twenty-one million, five hundred fifty-five thousand, nine hundred thirty-one".