21661660 has 12 divisors (see below), whose sum is σ = 45489528. Its totient is φ = 8664656.

The previous prime is 21661657. The next prime is 21661681. The reversal of 21661660 is 6616612.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 541522 + ... + 541561.

It is an arithmetic number, because the mean of its divisors is an integer number (3790794).

Almost surely, 2^21661660 is an apocalyptic number.

21661660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21661660 is an abundant number, since it is smaller than the sum of its proper divisors (23827868).

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

21661660 is a wasteful number, since it uses less digits than its factorization.

21661660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1083092 (or 1083090 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 28.

The square root of 21661660 is about 4654.2088479139. The cubic root of 21661660 is about 278.7600785969.

The spelling of 21661660 in words is "twenty-one million, six hundred sixty-one thousand, six hundred sixty".