21556530 has 56 divisors (see below), whose sum is σ = 58195692. Its totient is φ = 5746464.

The previous prime is 21556519. The next prime is 21556547. The reversal of 21556530 is 3565512.

21556530 is a `hidden beast` number, since 2 + 1 + 5 + 5 + 653 + 0 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 20331081 + 1225449 = 4509^2 + 1107^2 .

It is a super-4 number, since 4×21556530⁴ (a number of 30 digits) contains 4444 as substring.

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

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21556494 and 21556503.

It is an unprimeable number.

It is a polite number, since it can be written in 27 ways as a sum of consecutive naturals, for example, 5812 + ... + 8768.

Almost surely, 2^21556530 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21556530, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29097846).

21556530 is an abundant number, since it is smaller than the sum of its proper divisors (36639162).

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

21556530 is an equidigital number, since it uses as much as digits as its factorization.

21556530 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2982 (or 2967 counting only the distinct ones).

The product of its (nonzero) digits is 4500, while the sum is 27.

The square root of 21556530 is about 4642.9010327596. The cubic root of 21556530 is about 278.3083805982.

The spelling of 21556530 in words is "twenty-one million, five hundred fifty-six thousand, five hundred thirty".