21556021 has 2 divisors, whose sum is σ = 21556022. Its totient is φ = 21556020.

The previous prime is 21556009. The next prime is 21556027. The reversal of 21556021 is 12065512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18369796 + 3186225 = 4286^2 + 1785^2 .

It is a cyclic number.

It is not a de Polignac number, because 21556021 - 2⁷ = 21555893 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21555983 and 21556001.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21556027) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778010 + 10778011.

It is an arithmetic number, because the mean of its divisors is an integer number (10778011).

Almost surely, 2^21556021 is an apocalyptic number.

It is an amenable number.

21556021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21556021 is an equidigital number, since it uses as much as digits as its factorization.

21556021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 600, while the sum is 22.

The square root of 21556021 is about 4642.8462175696. The cubic root of 21556021 is about 278.3061900774.

The spelling of 21556021 in words is "twenty-one million, five hundred fifty-six thousand, twenty-one".