21658421 has 2 divisors, whose sum is σ = 21658422. Its totient is φ = 21658420.

The previous prime is 21658393. The next prime is 21658457. The reversal of 21658421 is 12485612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17757796 + 3900625 = 4214^2 + 1975^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21658421 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21658471) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10829210 + 10829211.

It is an arithmetic number, because the mean of its divisors is an integer number (10829211).

Almost surely, 2^21658421 is an apocalyptic number.

It is an amenable number.

21658421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21658421 is an equidigital number, since it uses as much as digits as its factorization.

21658421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3840, while the sum is 29.

The square root of 21658421 is about 4653.8608702882. The cubic root of 21658421 is about 278.7461838646.

The spelling of 21658421 in words is "twenty-one million, six hundred fifty-eight thousand, four hundred twenty-one".