21309760 has 28 divisors (see below), whose sum is σ = 50744628. Its totient is φ = 8523776.

The previous prime is 21309733. The next prime is 21309787. The reversal of 21309760 is 6790312.

It is an interprime number because it is at equal distance from previous prime (21309733) and next prime (21309787).

It can be written as a sum of positive squares in 2 ways, for example, as 7884864 + 13424896 = 2808^2 + 3664^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 32977 + ... + 33616.

Almost surely, 2^21309760 is an apocalyptic number.

21309760 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21309760 is an abundant number, since it is smaller than the sum of its proper divisors (29434868).

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

21309760 is an equidigital number, since it uses as much as digits as its factorization.

21309760 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66610 (or 66600 counting only the distinct ones).

The product of its (nonzero) digits is 2268, while the sum is 28.

The square root of 21309760 is about 4616.2495599783. The cubic root of 21309760 is about 277.2423168622.

The spelling of 21309760 in words is "twenty-one million, three hundred nine thousand, seven hundred sixty".