21617920 has 36 divisors (see below), whose sum is σ = 51784740. Its totient is φ = 8646656.

The previous prime is 21617909. The next prime is 21617927. The reversal of 21617920 is 2971612.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 3504384 + 18113536 = 1872^2 + 4256^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21617927) 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, 7165 + ... + 9724.

It is an arithmetic number, because the mean of its divisors is an integer number (1438465).

Almost surely, 2^21617920 is an apocalyptic number.

21617920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21617920 is an abundant number, since it is smaller than the sum of its proper divisors (30166820).

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

21617920 is an equidigital number, since it uses as much as digits as its factorization.

21617920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16910 (or 16896 counting only the distinct ones).

The product of its (nonzero) digits is 1512, while the sum is 28.

The square root of 21617920 is about 4649.5075008005. The cubic root of 21617920 is about 278.5723247208.

The spelling of 21617920 in words is "twenty-one million, six hundred seventeen thousand, nine hundred twenty".