78542509 has 2 divisors, whose sum is σ = 78542510. Its totient is φ = 78542508.

The previous prime is 78542507. The next prime is 78542531. The reversal of 78542509 is 90524587.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 68525284 + 10017225 = 8278^2 + 3165^2 .

It is a cyclic number.

It is not a de Polignac number, because 78542509 - 2¹ = 78542507 is a prime.

Together with 78542507, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78542501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39271254 + 39271255.

It is an arithmetic number, because the mean of its divisors is an integer number (39271255).

Almost surely, 2^78542509 is an apocalyptic number.

It is an amenable number.

78542509 is a deficient number, since it is larger than the sum of its proper divisors (1).

78542509 is an equidigital number, since it uses as much as digits as its factorization.

78542509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 100800, while the sum is 40.

The square root of 78542509 is about 8862.4211703123. The cubic root of 78542509 is about 428.2541598261.

The spelling of 78542509 in words is "seventy-eight million, five hundred forty-two thousand, five hundred nine".