21851660 has 12 divisors (see below), whose sum is σ = 45888528. Its totient is φ = 8740656.

The previous prime is 21851657. The next prime is 21851671. The reversal of 21851660 is 6615812.

It is a happy number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 546272 + ... + 546311.

It is an arithmetic number, because the mean of its divisors is an integer number (3824044).

Almost surely, 2^21851660 is an apocalyptic number.

21851660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21851660 is an abundant number, since it is smaller than the sum of its proper divisors (24036868).

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

21851660 is a wasteful number, since it uses less digits than its factorization.

21851660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1092592 (or 1092590 counting only the distinct ones).

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

The square root of 21851660 is about 4674.5759165939. The cubic root of 21851660 is about 279.5727326948.

The spelling of 21851660 in words is "twenty-one million, eight hundred fifty-one thousand, six hundred sixty".