21138768 has 120 divisors (see below), whose sum is σ = 68838848. Its totient is φ = 5930496.

The previous prime is 21138751. The next prime is 21138781. The reversal of 21138768 is 86783112.

21138768 is a `hidden beast` number, since 211 + 387 + 68 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 67380 + ... + 67692.

Almost surely, 2^21138768 is an apocalyptic number.

21138768 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21138768, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34419424).

21138768 is an abundant number, since it is smaller than the sum of its proper divisors (47700080).

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

21138768 is a wasteful number, since it uses less digits than its factorization.

21138768 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 401 (or 392 counting only the distinct ones).

The product of its digits is 16128, while the sum is 36.

The square root of 21138768 is about 4597.6915947027. The cubic root of 21138768 is about 276.4987830041.

The spelling of 21138768 in words is "twenty-one million, one hundred thirty-eight thousand, seven hundred sixty-eight".