21720500 has 24 divisors (see below), whose sum is σ = 47438664. Its totient is φ = 8688000.

The previous prime is 21720499. The next prime is 21720511. The reversal of 21720500 is 502712.

21720500 = T₇ + T₈ + ... + T₅₀₆.

It can be written as a sum of positive squares in 4 ways, for example, as 1882384 + 19838116 = 1372^2 + 4454^2 .

It is a congruent number.

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, 21221 + ... + 22220.

It is an arithmetic number, because the mean of its divisors is an integer number (1976611).

Almost surely, 2^21720500 is an apocalyptic number.

21720500 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21720500 is an abundant number, since it is smaller than the sum of its proper divisors (25718164).

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

21720500 is a wasteful number, since it uses less digits than its factorization.

21720500 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43460 (or 43448 counting only the distinct ones).

The product of its (nonzero) digits is 140, while the sum is 17.

The square root of 21720500 is about 4660.5257214181. The cubic root of 21720500 is about 279.0122509319.

The spelling of 21720500 in words is "twenty-one million, seven hundred twenty thousand, five hundred".