78138509 has 2 divisors, whose sum is σ = 78138510. Its totient is φ = 78138508.

The previous prime is 78138493. The next prime is 78138517. The reversal of 78138509 is 90583187.

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., 66373609 + 11764900 = 8147^2 + 3430^2 .

It is an emirp because it is prime and its reverse (90583187) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 78138509 - 2⁴ = 78138493 is a prime.

It is a super-2 number, since 2×78138509² = 12211253177486162, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78138539) 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, 39069254 + 39069255.

It is an arithmetic number, because the mean of its divisors is an integer number (39069255).

Almost surely, 2^78138509 is an apocalyptic number.

It is an amenable number.

78138509 is a deficient number, since it is larger than the sum of its proper divisors (1).

78138509 is an equidigital number, since it uses as much as digits as its factorization.

78138509 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 60480, while the sum is 41.

The square root of 78138509 is about 8839.5989162405. The cubic root of 78138509 is about 427.5186253185.

The spelling of 78138509 in words is "seventy-eight million, one hundred thirty-eight thousand, five hundred nine".