21720507 has 12 divisors (see below), whose sum is σ = 29997240. Its totient is φ = 13979392.

The previous prime is 21720499. The next prime is 21720511. The reversal of 21720507 is 70502712.

It is not a de Polignac number, because 21720507 - 2³ = 21720499 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21720007) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1782 + ... + 6827.

It is an arithmetic number, because the mean of its divisors is an integer number (2499770).

Almost surely, 2^21720507 is an apocalyptic number.

21720507 is a deficient number, since it is larger than the sum of its proper divisors (8276733).

21720507 is an equidigital number, since it uses as much as digits as its factorization.

21720507 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8670 (or 8641 counting only the distinct ones).

The product of its (nonzero) digits is 980, while the sum is 24.

The square root of 21720507 is about 4660.5264724063. The cubic root of 21720507 is about 279.0122809049.

The spelling of 21720507 in words is "twenty-one million, seven hundred twenty thousand, five hundred seven".