216531509 has 2 divisors, whose sum is σ = 216531510. Its totient is φ = 216531508.

The previous prime is 216531493. The next prime is 216531521. The reversal of 216531509 is 905135612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 112042225 + 104489284 = 10585^2 + 10222^2 .

It is a cyclic number.

It is not a de Polignac number, because 216531509 - 2⁴ = 216531493 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (216531529) 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 as a sum of consecutive naturals, namely, 108265754 + 108265755.

It is an arithmetic number, because the mean of its divisors is an integer number (108265755).

Almost surely, 2^216531509 is an apocalyptic number.

It is an amenable number.

216531509 is a deficient number, since it is larger than the sum of its proper divisors (1).

216531509 is an equidigital number, since it uses as much as digits as its factorization.

216531509 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 8100, while the sum is 32.

The square root of 216531509 is about 14715.0096500138. The cubic root of 216531509 is about 600.4917348476.

The spelling of 216531509 in words is "two hundred sixteen million, five hundred thirty-one thousand, five hundred nine".