21681256 has 16 divisors (see below), whose sum is σ = 43043940. Its totient is φ = 10202880.

The previous prime is 21681221. The next prime is 21681269. The reversal of 21681256 is 65218612.

It can be written as a sum of positive squares in 2 ways, for example, as 19624900 + 2056356 = 4430^2 + 1434^2 .

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 3 ways as a sum of consecutive naturals, for example, 79575 + ... + 79846.

Almost surely, 2^21681256 is an apocalyptic number.

It is an amenable number.

21681256 is a deficient number, since it is larger than the sum of its proper divisors (21362684).

21681256 is a wasteful number, since it uses less digits than its factorization.

21681256 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 159444 (or 159440 counting only the distinct ones).

The product of its digits is 5760, while the sum is 31.

The square root of 21681256 is about 4656.3135633245. The cubic root of 21681256 is about 278.8441124168.

Adding to 21681256 its reverse (65218612), we get a palindrome (86899868).

The spelling of 21681256 in words is "twenty-one million, six hundred eighty-one thousand, two hundred fifty-six".