21008515 has 16 divisors (see below), whose sum is σ = 29121120. Its totient is φ = 14379520.

The previous prime is 21008503. The next prime is 21008521. The reversal of 21008515 is 51580012.

It is not a de Polignac number, because 21008515 - 2¹⁷ = 20877443 is a prime.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10300 + ... + 12169.

It is an arithmetic number, because the mean of its divisors is an integer number (1820070).

Almost surely, 2^21008515 is an apocalyptic number.

21008515 is a deficient number, since it is larger than the sum of its proper divisors (8112605).

21008515 is a wasteful number, since it uses less digits than its factorization.

21008515 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22502.

The product of its (nonzero) digits is 400, while the sum is 22.

The square root of 21008515 is about 4583.5046634644. The cubic root of 21008515 is about 275.9297018681.

Adding to 21008515 its reverse (51580012), we get a palindrome (72588527).

The spelling of 21008515 in words is "twenty-one million, eight thousand, five hundred fifteen".