21379644 has 72 divisors (see below), whose sum is σ = 63506352. Its totient is φ = 5978880.

The previous prime is 21379619. The next prime is 21379663. The reversal of 21379644 is 44697312.

21379644 is a `hidden beast` number, since 2 + 1 + 3 + 7 + 9 + 644 = 666.

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

It is a junction number, because it is equal to n+sod(n) for n = 21379599 and 21379608.

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, 3072 + ... + 7224.

Almost surely, 2^21379644 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 21379644, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31753176).

21379644 is an abundant number, since it is smaller than the sum of its proper divisors (42126708).

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

21379644 is a wasteful number, since it uses less digits than its factorization.

21379644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4187 (or 4182 counting only the distinct ones).

The product of its digits is 36288, while the sum is 36.

The square root of 21379644 is about 4623.8127124701. The cubic root of 21379644 is about 277.5450523396.

It can be divided in two parts, 2137 and 9644, that added together give a triangular number (11781 = T₁₅₃).

The spelling of 21379644 in words is "twenty-one million, three hundred seventy-nine thousand, six hundred forty-four".