21061656 has 192 divisors, whose sum is σ = 74131200. Its totient is φ = 5241600.

The previous prime is 21061639. The next prime is 21061669. The reversal of 21061656 is 65616012.

It is a happy number.

21061656 is a `hidden beast` number, since 2 + 1 + 0 + 6 + 1 + 656 = 666.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 160711 + ... + 160841.

It is an arithmetic number, because the mean of its divisors is an integer number (386100).

Almost surely, 2^21061656 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 21061656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37065600).

21061656 is an abundant number, since it is smaller than the sum of its proper divisors (53069544).

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

21061656 is a wasteful number, since it uses less digits than its factorization.

21061656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 190 (or 183 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 21061656 is about 4589.2979855311. The cubic root of 21061656 is about 276.1621605344.

Adding to 21061656 its reverse (65616012), we get a palindrome (86677668).

The spelling of 21061656 in words is "twenty-one million, sixty-one thousand, six hundred fifty-six".