21668945 has 8 divisors (see below), whose sum is σ = 26899560. Its totient is φ = 16737280.

The previous prime is 21668929. The next prime is 21668957. The reversal of 21668945 is 54986612.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 5764801 + 15904144 = 2401^2 + 3988^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21668945 - 2⁴ = 21668929 is a prime.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 74576 + ... + 74865.

It is an arithmetic number, because the mean of its divisors is an integer number (3362445).

Almost surely, 2^21668945 is an apocalyptic number.

It is an amenable number.

21668945 is a deficient number, since it is larger than the sum of its proper divisors (5230615).

21668945 is a wasteful number, since it uses less digits than its factorization.

21668945 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 149475.

The product of its digits is 103680, while the sum is 41.

The square root of 21668945 is about 4654.9914070812. The cubic root of 21668945 is about 278.7913248873.

It can be divided in two parts, 2166 and 8945, that added together give a palindrome (11111).

The spelling of 21668945 in words is "twenty-one million, six hundred sixty-eight thousand, nine hundred forty-five".