21720356 has 24 divisors (see below), whose sum is σ = 45997056. Its totient is φ = 8760960.

The previous prime is 21720317. The next prime is 21720371. The reversal of 21720356 is 65302712.

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, 22340 + ... + 23291.

It is an arithmetic number, because the mean of its divisors is an integer number (1916544).

Almost surely, 2^21720356 is an apocalyptic number.

It is an amenable number.

21720356 is an abundant number, since it is smaller than the sum of its proper divisors (24276700).

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

21720356 is a wasteful number, since it uses less digits than its factorization.

21720356 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 45659 (or 45657 counting only the distinct ones).

The product of its (nonzero) digits is 2520, while the sum is 26.

The square root of 21720356 is about 4660.5102724916. The cubic root of 21720356 is about 279.0116343431.

The spelling of 21720356 in words is "twenty-one million, seven hundred twenty thousand, three hundred fifty-six".