21656649 has 32 divisors (see below), whose sum is σ = 34974720. Its totient is φ = 11656512.

The previous prime is 21656629. The next prime is 21656671. The reversal of 21656649 is 94665612.

It is not a de Polignac number, because 21656649 - 2¹⁶ = 21591113 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21656629) 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 in 31 ways as a sum of consecutive naturals, for example, 25774 + ... + 26600.

It is an arithmetic number, because the mean of its divisors is an integer number (1092960).

Almost surely, 2^21656649 is an apocalyptic number.

21656649 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21656649 is a deficient number, since it is larger than the sum of its proper divisors (13318071).

21656649 is a wasteful number, since it uses less digits than its factorization.

21656649 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 909.

The product of its digits is 77760, while the sum is 39.

The square root of 21656649 is about 4653.6704868308. The cubic root of 21656649 is about 278.7385817144.

It can be divided in two parts, 216 and 56649, that added together give a palindrome (56865).

The spelling of 21656649 in words is "twenty-one million, six hundred fifty-six thousand, six hundred forty-nine".