216521305 has 32 divisors (see below), whose sum is σ = 348864768. Its totient is φ = 124588800.

The previous prime is 216521293. The next prime is 216521309. The reversal of 216521305 is 503125612.

It is not a de Polignac number, because 216521305 - 2⁷ = 216521177 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 216521305.

It is not an unprimeable number, because it can be changed into a prime (216521309) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 16626 + ... + 26635.

It is an arithmetic number, because the mean of its divisors is an integer number (10902024).

Almost surely, 2^216521305 is an apocalyptic number.

It is an amenable number.

216521305 is a deficient number, since it is larger than the sum of its proper divisors (132343463).

216521305 is a wasteful number, since it uses less digits than its factorization.

216521305 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43297.

The product of its (nonzero) digits is 1800, while the sum is 25.

The square root of 216521305 is about 14714.6629251234. The cubic root of 216521305 is about 600.4823020189.

Adding to 216521305 its reverse (503125612), we get a palindrome (719646917).

The spelling of 216521305 in words is "two hundred sixteen million, five hundred twenty-one thousand, three hundred five".