21724621 has 2 divisors, whose sum is σ = 21724622. Its totient is φ = 21724620.

The previous prime is 21724613. The next prime is 21724649. The reversal of 21724621 is 12642712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20702500 + 1022121 = 4550^2 + 1011^2 .

It is a cyclic number.

It is not a de Polignac number, because 21724621 - 2³ = 21724613 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21724321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10862310 + 10862311.

It is an arithmetic number, because the mean of its divisors is an integer number (10862311).

Almost surely, 2^21724621 is an apocalyptic number.

It is an amenable number.

21724621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21724621 is an equidigital number, since it uses as much as digits as its factorization.

21724621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1344, while the sum is 25.

The square root of 21724621 is about 4660.9678179537. The cubic root of 21724621 is about 279.0298953504.

The spelling of 21724621 in words is "twenty-one million, seven hundred twenty-four thousand, six hundred twenty-one".