21561144 has 32 divisors (see below), whose sum is σ = 58803840. Its totient is φ = 6533600.

The previous prime is 21561131. The next prime is 21561167. The reversal of 21561144 is 44116512.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 40572 + ... + 41099.

It is an arithmetic number, because the mean of its divisors is an integer number (1837620).

Almost surely, 2^21561144 is an apocalyptic number.

21561144 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21561144 is an abundant number, since it is smaller than the sum of its proper divisors (37242696).

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

21561144 is a wasteful number, since it uses less digits than its factorization.

21561144 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 81691 (or 81687 counting only the distinct ones).

The product of its digits is 960, while the sum is 24.

The square root of 21561144 is about 4643.3978937842. The cubic root of 21561144 is about 278.3282357304.

Adding to 21561144 its reverse (44116512), we get a palindrome (65677656).

It can be divided in two parts, 21 and 561144, that added together give a palindrome (561165).

The spelling of 21561144 in words is "twenty-one million, five hundred sixty-one thousand, one hundred forty-four".