21387256 has 32 divisors (see below), whose sum is σ = 44686080. Its totient is φ = 9512800.

The previous prime is 21387251. The next prime is 21387257. The reversal of 21387256 is 65278312.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21387251) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1551 + ... + 6721.

It is an arithmetic number, because the mean of its divisors is an integer number (1396440).

Almost surely, 2^21387256 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21387256, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22343040).

21387256 is an abundant number, since it is smaller than the sum of its proper divisors (23298824).

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

21387256 is a wasteful number, since it uses less digits than its factorization.

21387256 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5235 (or 5231 counting only the distinct ones).

The product of its digits is 20160, while the sum is 34.

The square root of 21387256 is about 4624.6357694417. The cubic root of 21387256 is about 277.5779874414.

The spelling of 21387256 in words is "twenty-one million, three hundred eighty-seven thousand, two hundred fifty-six".