21720980 has 24 divisors (see below), whose sum is σ = 46728360. Its totient is φ = 8476160.

The previous prime is 21720953. The next prime is 21720983. The reversal of 21720980 is 8902712.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 228484 + 21492496 = 478^2 + 4636^2 .

It is a zygodrome in base 9.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720983) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12425 + ... + 14064.

It is an arithmetic number, because the mean of its divisors is an integer number (1947015).

Almost surely, 2^21720980 is an apocalyptic number.

21720980 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21720980 is an abundant number, since it is smaller than the sum of its proper divisors (25007380).

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

21720980 is a wasteful number, since it uses less digits than its factorization.

21720980 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26539 (or 26537 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 29.

The square root of 21720980 is about 4660.5772174700. The cubic root of 21720980 is about 279.0143062083.

The spelling of 21720980 in words is "twenty-one million, seven hundred twenty thousand, nine hundred eighty".