21633681 has 16 divisors (see below), whose sum is σ = 30038400. Its totient is φ = 13832448.

The previous prime is 21633679. The next prime is 21633683. The reversal of 21633681 is 18633612.

It is an interprime number because it is at equal distance from previous prime (21633679) and next prime (21633683).

It is not a de Polignac number, because 21633681 - 2¹ = 21633679 is a prime.

It is a super-2 number, since 2×21633681² = 936032307219522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21633683) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13785 + ... + 15273.

It is an arithmetic number, because the mean of its divisors is an integer number (1877400).

Almost surely, 2^21633681 is an apocalyptic number.

It is an amenable number.

21633681 is a deficient number, since it is larger than the sum of its proper divisors (8404719).

21633681 is a wasteful number, since it uses less digits than its factorization.

21633681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1688.

The product of its digits is 5184, while the sum is 30.

The square root of 21633681 is about 4651.2021026827. The cubic root of 21633681 is about 278.6400079489.

The spelling of 21633681 in words is "twenty-one million, six hundred thirty-three thousand, six hundred eighty-one".