21656646 has 48 divisors (see below), whose sum is σ = 53097408. Its totient is φ = 6561000.

The previous prime is 21656629. The next prime is 21656671. The reversal of 21656646 is 64665612.

It is a happy number.

21656646 is a `hidden beast` number, since 2 + 1 + 6 + 5 + 6 + 646 = 666.

It is a self number, because there is not a number n which added to its sum of digits gives 21656646.

It is a congruent number.

It is an unprimeable number.

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 23 ways as a sum of consecutive naturals, for example, 3321 + ... + 7371.

It is an arithmetic number, because the mean of its divisors is an integer number (1106196).

Almost surely, 2^21656646 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21656646, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26548704).

21656646 is an abundant number, since it is smaller than the sum of its proper divisors (31440762).

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

21656646 is a wasteful number, since it uses less digits than its factorization.

21656646 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4079 (or 4067 counting only the distinct ones).

The product of its digits is 51840, while the sum is 36.

The square root of 21656646 is about 4653.6701645046. The cubic root of 21656646 is about 278.7385688436.

It can be divided in two parts, 216566 and 46, that added together give a palindrome (216612).

The spelling of 21656646 in words is "twenty-one million, six hundred fifty-six thousand, six hundred forty-six".