216509 has 2 divisors, whose sum is σ = 216510. Its totient is φ = 216508.

The previous prime is 216493. The next prime is 216523. The reversal of 216509 is 905612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 120409 + 96100 = 347^2 + 310^2 .

It is a cyclic number.

It is not a de Polignac number, because 216509 - 2⁴ = 216493 is a prime.

It is a super-2 number, since 2×216509² = 93752294162, which contains 22 as substring.

It is a Chen prime.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (216569) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108254 + 108255.

It is an arithmetic number, because the mean of its divisors is an integer number (108255).

2²¹⁶⁵⁰⁹ is an apocalyptic number.

It is an amenable number.

216509 is a deficient number, since it is larger than the sum of its proper divisors (1).

216509 is an equidigital number, since it uses as much as digits as its factorization.

216509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 216509 is about 465.3052761360. The cubic root of 216509 is about 60.0470926580.

The spelling of 216509 in words is "two hundred sixteen thousand, five hundred nine".