21217305 has 16 divisors (see below), whose sum is σ = 34030080. Its totient is φ = 11288448.

The previous prime is 21217289. The next prime is 21217307. The reversal of 21217305 is 50371212.

It is not a de Polignac number, because 21217305 - 2⁴ = 21217289 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21217307) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5709 + ... + 8661.

It is an arithmetic number, because the mean of its divisors is an integer number (2126880).

Almost surely, 2^21217305 is an apocalyptic number.

It is an amenable number.

21217305 is a deficient number, since it is larger than the sum of its proper divisors (12812775).

21217305 is a wasteful number, since it uses less digits than its factorization.

21217305 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3440.

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 21217305 is about 4606.2245928743. The cubic root of 21217305 is about 276.8407857040.

Adding to 21217305 its reverse (50371212), we get a palindrome (71588517).

The spelling of 21217305 in words is "twenty-one million, two hundred seventeen thousand, three hundred five".