21705980 has 36 divisors (see below), whose sum is σ = 48183240. Its totient is φ = 8191008.

The previous prime is 21705977. The next prime is 21706019. The reversal of 21705980 is 8950712.

It is a super-2 number, since 2×21705980² = 942299135520800, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 90701 + ... + 90939.

Almost surely, 2^21705980 is an apocalyptic number.

21705980 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21705980, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24091620).

21705980 is an abundant number, since it is smaller than the sum of its proper divisors (26477260).

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

21705980 is a wasteful number, since it uses less digits than its factorization.

21705980 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 506 (or 265 counting only the distinct ones).

The product of its (nonzero) digits is 5040, while the sum is 32.

The square root of 21705980 is about 4658.9676968187. The cubic root of 21705980 is about 278.9500645034.

The spelling of 21705980 in words is "twenty-one million, seven hundred five thousand, nine hundred eighty".