21138688 has 36 divisors (see below), whose sum is σ = 42825888. Its totient is φ = 10411520.

The previous prime is 21138619. The next prime is 21138713. The reversal of 21138688 is 88683112.

It is a super-2 number, since 2×21138688² = 893688260722688, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17595 + ... + 18757.

It is an arithmetic number, because the mean of its divisors is an integer number (1189608).

Almost surely, 2^21138688 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21138688, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21412944).

21138688 is an abundant number, since it is smaller than the sum of its proper divisors (21687200).

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

21138688 is an equidigital number, since it uses as much as digits as its factorization.

21138688 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1250 (or 1236 counting only the distinct ones).

The product of its digits is 18432, while the sum is 37.

The square root of 21138688 is about 4597.6828946764. The cubic root of 21138688 is about 276.4984341990.

It can be divided in two parts, 2113 and 8688, that added together give a palindrome (10801).

The spelling of 21138688 in words is "twenty-one million, one hundred thirty-eight thousand, six hundred eighty-eight".