21664225 has 12 divisors (see below), whose sum is σ = 29306160. Its totient is φ = 15755600.

The previous prime is 21664207. The next prime is 21664267. The reversal of 21664225 is 52246612.

It is not a de Polignac number, because 21664225 - 2⁵ = 21664193 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21664193 and 21664202.

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 11 ways as a sum of consecutive naturals, for example, 39115 + ... + 39664.

It is an arithmetic number, because the mean of its divisors is an integer number (2442180).

Almost surely, 2^21664225 is an apocalyptic number.

21664225 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21664225 is a deficient number, since it is larger than the sum of its proper divisors (7641935).

21664225 is a wasteful number, since it uses less digits than its factorization.

21664225 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 78800 (or 78795 counting only the distinct ones).

The product of its digits is 5760, while the sum is 28.

The square root of 21664225 is about 4654.4843967941. The cubic root of 21664225 is about 278.7710810067.

The spelling of 21664225 in words is "twenty-one million, six hundred sixty-four thousand, two hundred twenty-five".