21681560 has 32 divisors (see below), whose sum is σ = 50468400. Its totient is φ = 8373120.

The previous prime is 21681553. The next prime is 21681599. The reversal of 21681560 is 6518612.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (29).

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, 8186 + ... + 10505.

Almost surely, 2^21681560 is an apocalyptic number.

21681560 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21681560 is an abundant number, since it is smaller than the sum of its proper divisors (28786840).

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

21681560 is a wasteful number, since it uses less digits than its factorization.

21681560 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18731 (or 18727 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 29.

The square root of 21681560 is about 4656.3462070598. The cubic root of 21681560 is about 278.8454156656.

The spelling of 21681560 in words is "twenty-one million, six hundred eighty-one thousand, five hundred sixty".