21287232 has 112 divisors (see below), whose sum is σ = 63723520. Its totient is φ = 6967296.

The previous prime is 21287221. The next prime is 21287243. The reversal of 21287232 is 23278212.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21287221) and next prime (21287243).

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

It is a junction number, because it is equal to n+sod(n) for n = 21287196 and 21287205.

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, 167553 + ... + 167679.

It is an arithmetic number, because the mean of its divisors is an integer number (568960).

Almost surely, 2^21287232 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 21287232, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31861760).

21287232 is an abundant number, since it is smaller than the sum of its proper divisors (42436288).

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

21287232 is a wasteful number, since it uses less digits than its factorization.

21287232 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 245 (or 229 counting only the distinct ones).

The product of its digits is 2688, while the sum is 27.

The square root of 21287232 is about 4613.8088386928. The cubic root of 21287232 is about 277.1445851635.

The spelling of 21287232 in words is "twenty-one million, two hundred eighty-seven thousand, two hundred thirty-two".