21707640 has 96 divisors (see below), whose sum is σ = 74720880. Its totient is φ = 5446656.

The previous prime is 21707603. The next prime is 21707701. The reversal of 21707640 is 4670712.

21707640 is a `hidden beast` number, since 2 + 17 + 0 + 7 + 640 = 666.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4347 + ... + 7893.

Almost surely, 2^21707640 is an apocalyptic number.

21707640 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 21707640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37360440).

21707640 is an abundant number, since it is smaller than the sum of its proper divisors (53013240).

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

21707640 is a wasteful number, since it uses less digits than its factorization.

21707640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3581 (or 3574 counting only the distinct ones).

The product of its (nonzero) digits is 2352, while the sum is 27.

The square root of 21707640 is about 4659.1458444655. The cubic root of 21707640 is about 278.9571753749.

The spelling of 21707640 in words is "twenty-one million, seven hundred seven thousand, six hundred forty".