21664168 has 16 divisors (see below), whose sum is σ = 40942080. Its totient is φ = 10746288.

The previous prime is 21664163. The next prime is 21664169. The reversal of 21664168 is 86146612.

It is a super-3 number, since 3×21664168³ (a number of 23 digits) contains 333 as substring.

It is not an unprimeable number, because it can be changed into a prime (21664163) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9646 + ... + 11677.

It is an arithmetic number, because the mean of its divisors is an integer number (2558880).

Almost surely, 2^21664168 is an apocalyptic number.

It is an amenable number.

21664168 is a deficient number, since it is larger than the sum of its proper divisors (19277912).

21664168 is a wasteful number, since it uses less digits than its factorization.

21664168 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21456 (or 21452 counting only the distinct ones).

The product of its digits is 13824, while the sum is 34.

The square root of 21664168 is about 4654.4782736629. The cubic root of 21664168 is about 278.7708365181.

It can be divided in two parts, 2166416 and 8, that multiplied together give a triangular number (17331328 = T₅₈₈₇).

The spelling of 21664168 in words is "twenty-one million, six hundred sixty-four thousand, one hundred sixty-eight".