21305515 has 16 divisors (see below), whose sum is σ = 31875840. Its totient is φ = 13281120.

The previous prime is 21305513. The next prime is 21305533. The reversal of 21305515 is 51550312.

It is not a de Polignac number, because 21305515 - 2¹ = 21305513 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21305513) 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, 27285 + ... + 28054.

It is an arithmetic number, because the mean of its divisors is an integer number (1992240).

Almost surely, 2^21305515 is an apocalyptic number.

21305515 is a deficient number, since it is larger than the sum of its proper divisors (10570325).

21305515 is a wasteful number, since it uses less digits than its factorization.

21305515 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55362.

The product of its (nonzero) digits is 750, while the sum is 22.

The square root of 21305515 is about 4615.7897482446. The cubic root of 21305515 is about 277.2239063343.

Adding to 21305515 its reverse (51550312), we get a palindrome (72855827).

The spelling of 21305515 in words is "twenty-one million, three hundred five thousand, five hundred fifteen".