21530287 has 4 divisors (see below), whose sum is σ = 22663480. Its totient is φ = 20397096.

The previous prime is 21530281. The next prime is 21530291. The reversal of 21530287 is 78203512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21530287 - 2¹⁵ = 21497519 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21530281) 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, 566568 + ... + 566605.

It is an arithmetic number, because the mean of its divisors is an integer number (5665870).

Almost surely, 2^21530287 is an apocalyptic number.

21530287 is a deficient number, since it is larger than the sum of its proper divisors (1133193).

21530287 is a wasteful number, since it uses less digits than its factorization.

21530287 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1133192.

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

The square root of 21530287 is about 4640.0740295819. The cubic root of 21530287 is about 278.1953968501.

Adding to 21530287 its reverse (78203512), we get a palindrome (99733799).

The spelling of 21530287 in words is "twenty-one million, five hundred thirty thousand, two hundred eighty-seven".