21287530 has 48 divisors (see below), whose sum is σ = 42871752. Its totient is φ = 7603200.

The previous prime is 21287459. The next prime is 21287531. The reversal of 21287530 is 3578212.

It can be written as a sum of positive squares in 4 ways, for example, as 19456921 + 1830609 = 4411^2 + 1353^2 .

It is a Smith number, since the sum of its digits (28) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (21287531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 88210 + ... + 88450.

Almost surely, 2^21287530 is an apocalyptic number.

21287530 is an abundant number, since it is smaller than the sum of its proper divisors (21584222).

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

21287530 is a wasteful number, since it uses less digits than its factorization.

21287530 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 343 (or 332 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 28.

The square root of 21287530 is about 4613.8411329390. The cubic root of 21287530 is about 277.1458784067.

The spelling of 21287530 in words is "twenty-one million, two hundred eighty-seven thousand, five hundred thirty".