78509 has 2 divisors, whose sum is σ = 78510. Its totient is φ = 78508.

The previous prime is 78497. The next prime is 78511. The reversal of 78509 is 90587.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 77284 + 1225 = 278^2 + 35^2 .

It is a cyclic number.

It is not a de Polignac number, because 78509 - 2¹² = 74413 is a prime.

It is a Sophie Germain prime.

Together with 78511, it forms a pair of twin primes.

It is a Chen prime.

It is an Ulam number.

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

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78539) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39254 + 39255.

It is an arithmetic number, because the mean of its divisors is an integer number (39255).

2⁷⁸⁵⁰⁹ is an apocalyptic number.

It is an amenable number.

78509 is a deficient number, since it is larger than the sum of its proper divisors (1).

78509 is an equidigital number, since it uses as much as digits as its factorization.

78509 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2520, while the sum is 29.

The square root of 78509 is about 280.1945752508. The cubic root of 78509 is about 42.8193248395.

The spelling of 78509 in words is "seventy-eight thousand, five hundred nine".