21563657 has 4 divisors (see below), whose sum is σ = 21629136. Its totient is φ = 21498180.

The previous prime is 21563639. The next prime is 21563699. The reversal of 21563657 is 75636512.

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 21563657 - 2¹⁰ = 21562633 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21563057) 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, 32243 + ... + 32904.

It is an arithmetic number, because the mean of its divisors is an integer number (5407284).

Almost surely, 2^21563657 is an apocalyptic number.

It is an amenable number.

21563657 is a deficient number, since it is larger than the sum of its proper divisors (65479).

21563657 is an equidigital number, since it uses as much as digits as its factorization.

21563657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 65478.

The product of its digits is 37800, while the sum is 35.

The square root of 21563657 is about 4643.6684851527. The cubic root of 21563657 is about 278.3390485717.

The spelling of 21563657 in words is "twenty-one million, five hundred sixty-three thousand, six hundred fifty-seven".