21287168 has 54 divisors (see below), whose sum is σ = 49457646. Its totient is φ = 9117696.

The previous prime is 21287143. The next prime is 21287209. The reversal of 21287168 is 86178212.

It can be written as a sum of positive squares in only one way, i.e., 21086464 + 200704 = 4592^2 + 448^2 .

It is a zygodrome in base 3.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 11696 + ... + 13392.

Almost surely, 2^21287168 is an apocalyptic number.

21287168 is a gapful number since it is divisible by the number (28) 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 21287168, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24728823).

21287168 is an abundant number, since it is smaller than the sum of its proper divisors (28170478).

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

21287168 is an equidigital number, since it uses as much as digits as its factorization.

21287168 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1727 (or 1706 counting only the distinct ones).

The product of its digits is 10752, while the sum is 35.

The square root of 21287168 is about 4613.8019029863. The cubic root of 21287168 is about 277.1443074184.

The spelling of 21287168 in words is "twenty-one million, two hundred eighty-seven thousand, one hundred sixty-eight".