21164640 has 96 divisors (see below), whose sum is σ = 76204800. Its totient is φ = 4836864.

The previous prime is 21164593. The next prime is 21164659. The reversal of 21164640 is 4646112.

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 (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21164640.

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, 211 + ... + 6509.

It is an arithmetic number, because the mean of its divisors is an integer number (793800).

Almost surely, 2^21164640 is an apocalyptic number.

21164640 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 21164640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38102400).

21164640 is an abundant number, since it is smaller than the sum of its proper divisors (55040160).

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

21164640 is a wasteful number, since it uses less digits than its factorization.

21164640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6324 (or 6316 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 24.

The square root of 21164640 is about 4600.5043201806. The cubic root of 21164640 is about 276.6115404433.

The spelling of 21164640 in words is "twenty-one million, one hundred sixty-four thousand, six hundred forty".