21287900 has 36 divisors (see below), whose sum is σ = 46476192. Its totient is φ = 8463360.

The previous prime is 21287879. The next prime is 21287909. The reversal of 21287900 is 978212.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21287909) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 18749 + ... + 19851.

Almost surely, 2^21287900 is an apocalyptic number.

21287900 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 21287900, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23238096).

21287900 is an abundant number, since it is smaller than the sum of its proper divisors (25188292).

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

21287900 is a wasteful number, since it uses less digits than its factorization.

21287900 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1310 (or 1303 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 29.

The square root of 21287900 is about 4613.8812295073. The cubic root of 21287900 is about 277.1474840944.

The spelling of 21287900 in words is "twenty-one million, two hundred eighty-seven thousand, nine hundred".