21908640 has 96 divisors (see below), whose sum is σ = 74342016. Its totient is φ = 5391360.

The previous prime is 21908611. The next prime is 21908651. The reversal of 21908640 is 4680912.

It is a tau number, because it is divible by the number of its divisors (96).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 21908598 and 21908607.

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, 4485 + ... + 7995.

It is an arithmetic number, because the mean of its divisors is an integer number (774396).

Almost surely, 2^21908640 is an apocalyptic number.

21908640 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 21908640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37171008).

21908640 is an abundant number, since it is smaller than the sum of its proper divisors (52433376).

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

21908640 is a wasteful number, since it uses less digits than its factorization.

21908640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3542 (or 3534 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 30.

The square root of 21908640 is about 4680.6666191900. Note that the first 4 decimals coincide. The cubic root of 21908640 is about 279.8155247455.

The spelling of 21908640 in words is "twenty-one million, nine hundred eight thousand, six hundred forty".