21642563 has 4 divisors (see below), whose sum is σ = 22583568. Its totient is φ = 20701560.

The previous prime is 21642559. The next prime is 21642587. The reversal of 21642563 is 36524612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21642563 - 2² = 21642559 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21642503) 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, 470468 + ... + 470513.

It is an arithmetic number, because the mean of its divisors is an integer number (5645892).

Almost surely, 2^21642563 is an apocalyptic number.

21642563 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

21642563 is a deficient number, since it is larger than the sum of its proper divisors (941005).

21642563 is an equidigital number, since it uses as much as digits as its factorization.

21642563 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 941004.

The product of its digits is 8640, while the sum is 29.

The square root of 21642563 is about 4652.1568116305. The cubic root of 21642563 is about 278.6781358712.

The spelling of 21642563 in words is "twenty-one million, six hundred forty-two thousand, five hundred sixty-three".