21668481 has 24 divisors (see below), whose sum is σ = 32933160. Its totient is φ = 13708800.

The previous prime is 21668477. The next prime is 21668483. The reversal of 21668481 is 18486612.

It can be written as a sum of positive squares in 4 ways, for example, as 129600 + 21538881 = 360^2 + 4641^2 .

It is not a de Polignac number, because 21668481 - 2² = 21668477 is a prime.

It is a super-2 number, since 2×21668481² = 939046137694722, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21668483) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 15241 + ... + 16601.

It is an arithmetic number, because the mean of its divisors is an integer number (1372215).

Almost surely, 2^21668481 is an apocalyptic number.

It is an amenable number.

21668481 is a deficient number, since it is larger than the sum of its proper divisors (11264679).

21668481 is a wasteful number, since it uses less digits than its factorization.

21668481 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1457 (or 1454 counting only the distinct ones).

The product of its digits is 18432, while the sum is 36.

The square root of 21668481 is about 4654.9415678395. The cubic root of 21668481 is about 278.7893349412.

The spelling of 21668481 in words is "twenty-one million, six hundred sixty-eight thousand, four hundred eighty-one".