21609756 has 72 divisors (see below), whose sum is σ = 64602720. Its totient is φ = 5959296.

The previous prime is 21609733. The next prime is 21609767. The reversal of 21609756 is 65790612.

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

21609756 is a modest number, since divided by 9756 gives 216 as remainder.

It is a self number, because there is not a number n which added to its sum of digits gives 21609756.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 5830 + ... + 8786.

It is an arithmetic number, because the mean of its divisors is an integer number (897260).

Almost surely, 2^21609756 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 21609756, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32301360).

21609756 is an abundant number, since it is smaller than the sum of its proper divisors (42992964).

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

21609756 is a wasteful number, since it uses less digits than its factorization.

21609756 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3003 (or 2998 counting only the distinct ones).

The product of its (nonzero) digits is 22680, while the sum is 36.

The square root of 21609756 is about 4648.6294754476. The cubic root of 21609756 is about 278.5372527248.

It can be divided in two parts, 216097 and 56, that added together give a triangular number (216153 = T₆₅₇).

The spelling of 21609756 in words is "twenty-one million, six hundred nine thousand, seven hundred fifty-six".