21053556 has 72 divisors (see below), whose sum is σ = 56818944. Its totient is φ = 6557760.

The previous prime is 21053537. The next prime is 21053563. The reversal of 21053556 is 65535012.

21053556 is a `hidden beast` number, since 2 + 105 + 3 + 556 = 666.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 38646 + ... + 39186.

It is an arithmetic number, because the mean of its divisors is an integer number (789152).

Almost surely, 2^21053556 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 21053556, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28409472).

21053556 is an abundant number, since it is smaller than the sum of its proper divisors (35765388).

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

21053556 is a wasteful number, since it uses less digits than its factorization.

21053556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 621 (or 616 counting only the distinct ones).

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

The square root of 21053556 is about 4588.4154127542. The cubic root of 21053556 is about 276.1267533736.

Adding to 21053556 its reverse (65535012), we get a palindrome (86588568).

It can be divided in two parts, 21053 and 556, that added together give a square (21609 = 147²).

The spelling of 21053556 in words is "twenty-one million, fifty-three thousand, five hundred fifty-six".