21280644 has 120 divisors (see below), whose sum is σ = 69440448. Its totient is φ = 5520960.

The previous prime is 21280639. The next prime is 21280687. The reversal of 21280644 is 44608212.

21280644 is a `hidden beast` number, since 2 + 12 + 8 + 0 + 644 = 666.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 24522 + ... + 25374.

Almost surely, 2^21280644 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 21280644, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34720224).

21280644 is an abundant number, since it is smaller than the sum of its proper divisors (48159804).

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

21280644 is a wasteful number, since it uses less digits than its factorization.

21280644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 887 (or 876 counting only the distinct ones).

The product of its (nonzero) digits is 3072, while the sum is 27.

The square root of 21280644 is about 4613.0948396928. The cubic root of 21280644 is about 277.1159918591.

Adding to 21280644 its reverse (44608212), we get a palindrome (65888856).

The spelling of 21280644 in words is "twenty-one million, two hundred eighty thousand, six hundred forty-four".