21768138 has 48 divisors (see below), whose sum is σ = 55650816. Its totient is φ = 6017760.

The previous prime is 21768133. The next prime is 21768179. The reversal of 21768138 is 83186712.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21768133) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1120 + ... + 6692.

It is an arithmetic number, because the mean of its divisors is an integer number (1159392).

Almost surely, 2^21768138 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21768138, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27825408).

21768138 is an abundant number, since it is smaller than the sum of its proper divisors (33882678).

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

21768138 is a wasteful number, since it uses less digits than its factorization.

21768138 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5619 (or 5616 counting only the distinct ones).

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

The square root of 21768138 is about 4665.6337190140. The cubic root of 21768138 is about 279.2160811119.

It can be divided in two parts, 2 and 1768138, that added together give a triangular number (1768140 = T₁₈₈₀).

The spelling of 21768138 in words is "twenty-one million, seven hundred sixty-eight thousand, one hundred thirty-eight".