21630561 has 4 divisors (see below), whose sum is σ = 28840752. Its totient is φ = 14420372.

The previous prime is 21630551. The next prime is 21630563. The reversal of 21630561 is 16503612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21630561 - 2²³ = 13241953 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21630563) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3605091 + ... + 3605096.

It is an arithmetic number, because the mean of its divisors is an integer number (7210188).

Almost surely, 2^21630561 is an apocalyptic number.

It is an amenable number.

21630561 is a deficient number, since it is larger than the sum of its proper divisors (7210191).

21630561 is an equidigital number, since it uses as much as digits as its factorization.

21630561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7210190.

The product of its (nonzero) digits is 1080, while the sum is 24.

The square root of 21630561 is about 4650.8666934239. The cubic root of 21630561 is about 278.6266121916.

The spelling of 21630561 in words is "twenty-one million, six hundred thirty thousand, five hundred sixty-one".