21287224 has 16 divisors (see below), whose sum is σ = 45615600. Its totient is φ = 9123072.

The previous prime is 21287221. The next prime is 21287243. The reversal of 21287224 is 42278212.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 21287192 and 21287201.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21287221) 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, 190009 + ... + 190120.

It is an arithmetic number, because the mean of its divisors is an integer number (2850975).

Almost surely, 2^21287224 is an apocalyptic number.

It is an amenable number.

21287224 is an abundant number, since it is smaller than the sum of its proper divisors (24328376).

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

21287224 is a wasteful number, since it uses less digits than its factorization.

21287224 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 380142 (or 380138 counting only the distinct ones).

The product of its digits is 3584, while the sum is 28.

The square root of 21287224 is about 4613.8079717301. The cubic root of 21287224 is about 277.1445504454.

The spelling of 21287224 in words is "twenty-one million, two hundred eighty-seven thousand, two hundred twenty-four".