21408656 has 10 divisors (see below), whose sum is σ = 41479302. Its totient is φ = 10704320.

The previous prime is 21408623. The next prime is 21408659. The reversal of 21408656 is 65680412.

It can be written as a sum of positive squares in only one way, i.e., 17472400 + 3936256 = 4180^2 + 1984^2 .

It is not an unprimeable number, because it can be changed into a prime (21408659) 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 as a sum of consecutive naturals, namely, 669005 + ... + 669036.

Almost surely, 2^21408656 is an apocalyptic number.

It is an amenable number.

21408656 is a deficient number, since it is larger than the sum of its proper divisors (20070646).

21408656 is a wasteful number, since it uses less digits than its factorization.

21408656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1338049 (or 1338043 counting only the distinct ones).

The product of its (nonzero) digits is 11520, while the sum is 32.

The square root of 21408656 is about 4626.9488866855. The cubic root of 21408656 is about 277.6705377090.

The spelling of 21408656 in words is "twenty-one million, four hundred eight thousand, six hundred fifty-six".