21338640 has 200 divisors, whose sum is σ = 76970520. Its totient is φ = 5474304.

The previous prime is 21338627. The next prime is 21338651. The reversal of 21338640 is 4683312.

It is a happy number.

21338640 is a `hidden beast` number, since 2 + 13 + 3 + 8 + 640 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 2985984 + 18352656 = 1728^2 + 4284^2 .

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 239716 + ... + 239804.

Almost surely, 2^21338640 is an apocalyptic number.

21338640 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 21338640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38485260).

21338640 is an abundant number, since it is smaller than the sum of its proper divisors (55631880).

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

21338640 is a wasteful number, since it uses less digits than its factorization.

21338640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 151 (or 136 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 27.

The square root of 21338640 is about 4619.3765813148. The cubic root of 21338640 is about 277.3675043160.

The spelling of 21338640 in words is "twenty-one million, three hundred thirty-eight thousand, six hundred forty".