21138684 has 96 divisors (see below), whose sum is σ = 60673536. Its totient is φ = 5591040.

The previous prime is 21138619. The next prime is 21138713. The reversal of 21138684 is 48683112.

It is a super-2 number, since 2×21138684² = 893687922503712, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 161299 + ... + 161429.

It is an arithmetic number, because the mean of its divisors is an integer number (632016).

Almost surely, 2^21138684 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 21138684, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30336768).

21138684 is an abundant number, since it is smaller than the sum of its proper divisors (39534852).

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

21138684 is a wasteful number, since it uses less digits than its factorization.

21138684 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 275 (or 273 counting only the distinct ones).

The product of its digits is 9216, while the sum is 33.

The square root of 21138684 is about 4597.6824596747. The cubic root of 21138684 is about 276.4984167587.

The spelling of 21138684 in words is "twenty-one million, one hundred thirty-eight thousand, six hundred eighty-four".