21555828 has 48 divisors (see below), whose sum is σ = 63871360. Its totient is φ = 6158592.

The previous prime is 21555817. The next prime is 21555829. The reversal of 21555828 is 82855512.

21555828 is a `hidden beast` number, since 21 + 55 + 582 + 8 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 21555792 and 21555801.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21555829) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13501 + ... + 15012.

Almost surely, 2^21555828 is an apocalyptic number.

21555828 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21555828 is an abundant number, since it is smaller than the sum of its proper divisors (42315532).

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

21555828 is a wasteful number, since it uses less digits than its factorization.

21555828 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28533 (or 28525 counting only the distinct ones).

The product of its digits is 32000, while the sum is 36.

The square root of 21555828 is about 4642.8254328587. The cubic root of 21555828 is about 278.3053594780.

The spelling of 21555828 in words is "twenty-one million, five hundred fifty-five thousand, eight hundred twenty-eight".