21516915 has 16 divisors (see below), whose sum is σ = 39345408. Its totient is φ = 9836256.

The previous prime is 21516893. The next prime is 21516919. The reversal of 21516915 is 51961512.

It is not a de Polignac number, because 21516915 - 2⁸ = 21516659 is a prime.

It is a super-2 number, since 2×21516915² = 925955262234450, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21516919) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 102357 + ... + 102566.

It is an arithmetic number, because the mean of its divisors is an integer number (2459088).

Almost surely, 2^21516915 is an apocalyptic number.

21516915 is a deficient number, since it is larger than the sum of its proper divisors (17828493).

21516915 is a wasteful number, since it uses less digits than its factorization.

21516915 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 204938.

The product of its digits is 2700, while the sum is 30.

The square root of 21516915 is about 4638.6328804940. The cubic root of 21516915 is about 278.1377911888.

The spelling of 21516915 in words is "twenty-one million, five hundred sixteen thousand, nine hundred fifteen".