21561156 has 36 divisors (see below), whose sum is σ = 55665792. Its totient is φ = 7033584.

The previous prime is 21561131. The next prime is 21561167. The reversal of 21561156 is 65116512.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (36).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 4680 + ... + 8063.

It is an arithmetic number, because the mean of its divisors is an integer number (1546272).

Almost surely, 2^21561156 is an apocalyptic number.

It is an amenable number.

21561156 is an abundant number, since it is smaller than the sum of its proper divisors (34104636).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21561156 is a wasteful number, since it uses less digits than its factorization.

21561156 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12800 (or 12795 counting only the distinct ones).

The product of its digits is 1800, while the sum is 27.

The square root of 21561156 is about 4643.3991859413. The cubic root of 21561156 is about 278.3282873655.

Adding to 21561156 its reverse (65116512), we get a palindrome (86677668).

The spelling of 21561156 in words is "twenty-one million, five hundred sixty-one thousand, one hundred fifty-six".