21608640 has 224 divisors, whose sum is σ = 79369920. Its totient is φ = 5529600.

The previous prime is 21608627. The next prime is 21608641. The reversal of 21608640 is 4680612.

21608640 is a `hidden beast` number, since 2 + 16 + 0 + 8 + 640 = 666.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a zygodrome in base 3.

It is not an unprimeable number, because it can be changed into a prime (21608641) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 354210 + ... + 354270.

It is an arithmetic number, because the mean of its divisors is an integer number (354330).

Almost surely, 2^21608640 is an apocalyptic number.

21608640 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 21608640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39684960).

21608640 is an abundant number, since it is smaller than the sum of its proper divisors (57761280).

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

21608640 is a wasteful number, since it uses less digits than its factorization.

21608640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 128 (or 112 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 27.

The square root of 21608640 is about 4648.5094385190. The cubic root of 21608640 is about 278.5324577775.

It can be divided in two parts, 2160 and 8640, that multiplied together give a square (18662400 = 4320²).

The spelling of 21608640 in words is "twenty-one million, six hundred eight thousand, six hundred forty".