21709656 has 48 divisors (see below), whose sum is σ = 59772960. Its totient is φ = 7116480.

The previous prime is 21709651. The next prime is 21709669. The reversal of 21709656 is 65690712.

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 21709656.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21709651) 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 11 ways as a sum of consecutive naturals, for example, 1921 + ... + 6863.

It is an arithmetic number, because the mean of its divisors is an integer number (1245270).

Almost surely, 2^21709656 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 21709656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29886480).

21709656 is an abundant number, since it is smaller than the sum of its proper divisors (38063304).

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

21709656 is a wasteful number, since it uses less digits than its factorization.

21709656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5016 (or 5009 counting only the distinct ones).

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

The square root of 21709656 is about 4659.3621881112. The cubic root of 21709656 is about 278.9658107410.

The spelling of 21709656 in words is "twenty-one million, seven hundred nine thousand, six hundred fifty-six".