21561320 has 32 divisors (see below), whose sum is σ = 52924320. Its totient is φ = 7840320.

The previous prime is 21561313. The next prime is 21561329. The reversal of 21561320 is 2316512.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a junction number, because it is equal to n+sod(n) for n = 21561292 and 21561301.

It is not an unprimeable number, because it can be changed into a prime (21561329) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 24062 + ... + 24941.

It is an arithmetic number, because the mean of its divisors is an integer number (1653885).

Almost surely, 2^21561320 is an apocalyptic number.

21561320 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21561320 is an abundant number, since it is smaller than the sum of its proper divisors (31363000).

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

21561320 is a wasteful number, since it uses less digits than its factorization.

21561320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49025 (or 49021 counting only the distinct ones).

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 21561320 is about 4643.4168453844. The cubic root of 21561320 is about 278.3289930439.

Adding to 21561320 its reverse (2316512), we get a palindrome (23877832).

The spelling of 21561320 in words is "twenty-one million, five hundred sixty-one thousand, three hundred twenty".