21902821 has 2 divisors, whose sum is σ = 21902822. Its totient is φ = 21902820.

The previous prime is 21902813. The next prime is 21902827. The reversal of 21902821 is 12820912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20930625 + 972196 = 4575^2 + 986^2 .

It is a cyclic number.

It is not a de Polignac number, because 21902821 - 2³ = 21902813 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21902827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10951410 + 10951411.

It is an arithmetic number, because the mean of its divisors is an integer number (10951411).

Almost surely, 2^21902821 is an apocalyptic number.

It is an amenable number.

21902821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21902821 is an equidigital number, since it uses as much as digits as its factorization.

21902821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 21902821 is about 4680.0449784163. The cubic root of 21902821 is about 279.7907492731.

The spelling of 21902821 in words is "twenty-one million, nine hundred two thousand, eight hundred twenty-one".