21315287 has 4 divisors (see below), whose sum is σ = 24360336. Its totient is φ = 18270240.

The previous prime is 21315271. The next prime is 21315289. The reversal of 21315287 is 78251312.

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 21315287 - 2⁴ = 21315271 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21315289) 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, 1522514 + ... + 1522527.

It is an arithmetic number, because the mean of its divisors is an integer number (6090084).

Almost surely, 2^21315287 is an apocalyptic number.

21315287 is a deficient number, since it is larger than the sum of its proper divisors (3045049).

21315287 is an equidigital number, since it uses as much as digits as its factorization.

21315287 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3045048.

The product of its digits is 3360, while the sum is 29.

The square root of 21315287 is about 4616.8481673107. The cubic root of 21315287 is about 277.2662837492.

Adding to 21315287 its reverse (78251312), we get a palindrome (99566599).

The spelling of 21315287 in words is "twenty-one million, three hundred fifteen thousand, two hundred eighty-seven".