21287644 has 12 divisors (see below), whose sum is σ = 42575344. Its totient is φ = 9123264.

The previous prime is 21287641. The next prime is 21287659. The reversal of 21287644 is 44678212.

It is a happy number.

21287644 is an admirable number.

It is a hoax number, since the sum of its digits (34) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21287641) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 380109 + ... + 380164.

Almost surely, 2^21287644 is an apocalyptic number.

It is an amenable number.

21287644 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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

21287644 is a wasteful number, since it uses less digits than its factorization.

21287644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 760284 (or 760282 counting only the distinct ones).

The product of its digits is 21504, while the sum is 34.

The square root of 21287644 is about 4613.8534870540. The cubic root of 21287644 is about 277.1463731341.

The spelling of 21287644 in words is "twenty-one million, two hundred eighty-seven thousand, six hundred forty-four".