21686563 has 2 divisors, whose sum is σ = 21686564. Its totient is φ = 21686562.

The previous prime is 21686557. The next prime is 21686579. The reversal of 21686563 is 36568612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21686563 - 2¹⁷ = 21555491 is a prime.

It is not a weakly prime, because it can be changed into another prime (21686513) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10843281 + 10843282.

It is an arithmetic number, because the mean of its divisors is an integer number (10843282).

Almost surely, 2^21686563 is an apocalyptic number.

21686563 is a deficient number, since it is larger than the sum of its proper divisors (1).

21686563 is an equidigital number, since it uses as much as digits as its factorization.

21686563 is an evil number, because the sum of its binary digits is even.

The product of its digits is 51840, while the sum is 37.

The square root of 21686563 is about 4656.8833998716. The cubic root of 21686563 is about 278.8668617904.

The spelling of 21686563 in words is "twenty-one million, six hundred eighty-six thousand, five hundred sixty-three".