21015287 has 4 divisors (see below), whose sum is σ = 21329016. Its totient is φ = 20701560.

The previous prime is 21015277. The next prime is 21015289. The reversal of 21015287 is 78251012.

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 21015287 - 2¹² = 21011191 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 (21015289) 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 3 ways as a sum of consecutive naturals, for example, 156764 + ... + 156897.

It is an arithmetic number, because the mean of its divisors is an integer number (5332254).

Almost surely, 2^21015287 is an apocalyptic number.

21015287 is a deficient number, since it is larger than the sum of its proper divisors (313729).

21015287 is an equidigital number, since it uses as much as digits as its factorization.

21015287 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 313728.

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 21015287 is about 4584.2433399635. The cubic root of 21015287 is about 275.9593469144.

Adding to 21015287 its reverse (78251012), we get a palindrome (99266299).

The spelling of 21015287 in words is "twenty-one million, fifteen thousand, two hundred eighty-seven".