21520305 has 24 divisors (see below), whose sum is σ = 37672128. Its totient is φ = 11363616.

The previous prime is 21520297. The next prime is 21520307. The reversal of 21520305 is 50302512.

It is a happy number.

It is not a de Polignac number, because 21520305 - 2³ = 21520297 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21520307) 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 23 ways as a sum of consecutive naturals, for example, 2314 + ... + 6956.

It is an arithmetic number, because the mean of its divisors is an integer number (1569672).

Almost surely, 2^21520305 is an apocalyptic number.

It is an amenable number.

21520305 is a deficient number, since it is larger than the sum of its proper divisors (16151823).

21520305 is a wasteful number, since it uses less digits than its factorization.

21520305 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4757 (or 4754 counting only the distinct ones).

The product of its (nonzero) digits is 300, while the sum is 18.

The square root of 21520305 is about 4638.9982754901. The cubic root of 21520305 is about 278.1523973347.

Adding to 21520305 its reverse (50302512), we get a palindrome (71822817).

The spelling of 21520305 in words is "twenty-one million, five hundred twenty thousand, three hundred five".