21015871 has 2 divisors, whose sum is σ = 21015872. Its totient is φ = 21015870.

The previous prime is 21015857. The next prime is 21015913. The reversal of 21015871 is 17851012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21015871 - 2¹¹ = 21013823 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21015851) 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 as a sum of consecutive naturals, namely, 10507935 + 10507936.

It is an arithmetic number, because the mean of its divisors is an integer number (10507936).

Almost surely, 2^21015871 is an apocalyptic number.

21015871 is a deficient number, since it is larger than the sum of its proper divisors (1).

21015871 is an equidigital number, since it uses as much as digits as its factorization.

21015871 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 560, while the sum is 25.

The square root of 21015871 is about 4584.3070359652. The cubic root of 21015871 is about 275.9619031292.

Adding to 21015871 its reverse (17851012), we get a palindrome (38866883).

The spelling of 21015871 in words is "twenty-one million, fifteen thousand, eight hundred seventy-one".