21565601 has 2 divisors, whose sum is σ = 21565602. Its totient is φ = 21565600.

The previous prime is 21565597. The next prime is 21565633. The reversal of 21565601 is 10656512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17007376 + 4558225 = 4124^2 + 2135^2 .

It is a cyclic number.

It is not a de Polignac number, because 21565601 - 2² = 21565597 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21561601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10782800 + 10782801.

It is an arithmetic number, because the mean of its divisors is an integer number (10782801).

Almost surely, 2^21565601 is an apocalyptic number.

It is an amenable number.

21565601 is a deficient number, since it is larger than the sum of its proper divisors (1).

21565601 is an equidigital number, since it uses as much as digits as its factorization.

21565601 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 21565601 is about 4643.8777977031. The cubic root of 21565601 is about 278.3474125650.

The spelling of 21565601 in words is "twenty-one million, five hundred sixty-five thousand, six hundred one".