21563531 has 16 divisors (see below), whose sum is σ = 25139808. Its totient is φ = 18430720.

The previous prime is 21563519. The next prime is 21563539. The reversal of 21563531 is 13536512.

It is not a de Polignac number, because 21563531 - 2⁶ = 21563467 is a prime.

It is a super-2 number, since 2×21563531² = 929971738375922, which contains 22 as substring.

It is a Duffinian number.

It is a zygodrome in base 11.

It is a self number, because there is not a number n which added to its sum of digits gives 21563531.

It is not an unprimeable number, because it can be changed into a prime (21563539) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 22151 + ... + 23103.

It is an arithmetic number, because the mean of its divisors is an integer number (1571238).

Almost surely, 2^21563531 is an apocalyptic number.

21563531 is a deficient number, since it is larger than the sum of its proper divisors (3576277).

21563531 is an equidigital number, since it uses as much as digits as its factorization.

21563531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1003 (or 981 counting only the distinct ones).

The product of its digits is 2700, while the sum is 26.

The square root of 21563531 is about 4643.6549182729. The cubic root of 21563531 is about 278.3385064437.

The spelling of 21563531 in words is "twenty-one million, five hundred sixty-three thousand, five hundred thirty-one".