21395556 has 144 divisors (see below), whose sum is σ = 69713280. Its totient is φ = 5624640.

The previous prime is 21395551. The next prime is 21395587. The reversal of 21395556 is 65559312.

21395556 is a `hidden beast` number, since 2 + 13 + 95 + 556 = 666.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21395556.

It is not an unprimeable number, because it can be changed into a prime (21395551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 68641 + ... + 68951.

It is an arithmetic number, because the mean of its divisors is an integer number (484120).

Almost surely, 2^21395556 is an apocalyptic number.

21395556 is a gapful number since it is divisible by the number (26) 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 21395556, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34856640).

21395556 is an abundant number, since it is smaller than the sum of its proper divisors (48317724).

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

21395556 is a wasteful number, since it uses less digits than its factorization.

21395556 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 351 (or 336 counting only the distinct ones).

The product of its digits is 40500, while the sum is 36.

The square root of 21395556 is about 4625.5330503630. The cubic root of 21395556 is about 277.6138904316.

The spelling of 21395556 in words is "twenty-one million, three hundred ninety-five thousand, five hundred fifty-six".