21684663 has 96 divisors (see below), whose sum is σ = 44029440. Its totient is φ = 9918720.

The previous prime is 21684661. The next prime is 21684679. The reversal of 21684663 is 36648612.

It is not a de Polignac number, because 21684663 - 2¹ = 21684661 is a prime.

It is a super-4 number, since 4×21684663⁴ (a number of 30 digits) contains 4444 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21684661) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 261220 + ... + 261302.

It is an arithmetic number, because the mean of its divisors is an integer number (458640).

Almost surely, 2^21684663 is an apocalyptic number.

21684663 is an abundant number, since it is smaller than the sum of its proper divisors (22344777).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21684663 is a wasteful number, since it uses less digits than its factorization.

21684663 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 149 (or 146 counting only the distinct ones).

The product of its digits is 41472, while the sum is 36.

The square root of 21684663 is about 4656.6793963081. The cubic root of 21684663 is about 278.8587175383.

The spelling of 21684663 in words is "twenty-one million, six hundred eighty-four thousand, six hundred sixty-three".