21012656 has 40 divisors (see below), whose sum is σ = 46854144. Its totient is φ = 8942400.

The previous prime is 21012653. The next prime is 21012661. The reversal of 21012656 is 65621012.

It is not an unprimeable number, because it can be changed into a prime (21012653) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 17681 + ... + 18831.

Almost surely, 2^21012656 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 21012656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23427072).

21012656 is an abundant number, since it is smaller than the sum of its proper divisors (25841488).

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

21012656 is a wasteful number, since it uses less digits than its factorization.

21012656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1329 (or 1323 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 21012656 is about 4583.9563697749. The cubic root of 21012656 is about 275.9478302291.

Adding to 21012656 its reverse (65621012), we get a palindrome (86633668).

The spelling of 21012656 in words is "twenty-one million, twelve thousand, six hundred fifty-six".