21905660 has 48 divisors (see below), whose sum is σ = 54867456. Its totient is φ = 7182912.

The previous prime is 21905647. The next prime is 21905687. The reversal of 21905660 is 6650912.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 182 + ... + 6621.

It is an arithmetic number, because the mean of its divisors is an integer number (1143072).

Almost surely, 2^21905660 is an apocalyptic number.

21905660 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 21905660, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27433728).

21905660 is an abundant number, since it is smaller than the sum of its proper divisors (32961796).

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

21905660 is a wasteful number, since it uses less digits than its factorization.

21905660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6842 (or 6840 counting only the distinct ones).

The product of its (nonzero) digits is 3240, while the sum is 29.

The square root of 21905660 is about 4680.3482776392. The cubic root of 21905660 is about 279.8028373906.

The spelling of 21905660 in words is "twenty-one million, nine hundred five thousand, six hundred sixty".