21569621 has 2 divisors, whose sum is σ = 21569622. Its totient is φ = 21569620.

The previous prime is 21569609. The next prime is 21569623. The reversal of 21569621 is 12696512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17724100 + 3845521 = 4210^2 + 1961^2 .

It is a cyclic number.

It is not a de Polignac number, because 21569621 - 2²² = 17375317 is a prime.

Together with 21569623, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21569623) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10784810 + 10784811.

It is an arithmetic number, because the mean of its divisors is an integer number (10784811).

Almost surely, 2^21569621 is an apocalyptic number.

It is an amenable number.

21569621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21569621 is an equidigital number, since it uses as much as digits as its factorization.

21569621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6480, while the sum is 32.

The square root of 21569621 is about 4644.3106054613. The cubic root of 21569621 is about 278.3647068829.

The spelling of 21569621 in words is "twenty-one million, five hundred sixty-nine thousand, six hundred twenty-one".