21664280 has 64 divisors (see below), whose sum is σ = 54237600. Its totient is φ = 7720960.

The previous prime is 21664267. The next prime is 21664297. The reversal of 21664280 is 8246612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 22856 + ... + 23784.

Almost surely, 2^21664280 is an apocalyptic number.

21664280 is a gapful number since it is divisible by the number (20) 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 21664280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27118800).

21664280 is an abundant number, since it is smaller than the sum of its proper divisors (32573320).

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

21664280 is a wasteful number, since it uses less digits than its factorization.

21664280 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1004 (or 1000 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 29.

The square root of 21664280 is about 4654.4903050710. The cubic root of 21664280 is about 278.7713169163.

It can be divided in two parts, 2166 and 4280, that added together give a palindrome (6446).

The spelling of 21664280 in words is "twenty-one million, six hundred sixty-four thousand, two hundred eighty".