78391309 has 2 divisors, whose sum is σ = 78391310. Its totient is φ = 78391308.

The previous prime is 78391307. The next prime is 78391349. The reversal of 78391309 is 90319387.

It is an a-pointer prime, because the next prime (78391349) can be obtained adding 78391309 to its sum of digits (40).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 78057225 + 334084 = 8835^2 + 578^2 .

It is an emirp because it is prime and its reverse (90319387) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 78391309 - 2¹ = 78391307 is a prime.

It is a super-2 number, since 2×78391309² = 12290394653466962, which contains 22 as substring.

Together with 78391307, 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 (78391307) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39195654 + 39195655.

It is an arithmetic number, because the mean of its divisors is an integer number (39195655).

Almost surely, 2^78391309 is an apocalyptic number.

It is an amenable number.

78391309 is a deficient number, since it is larger than the sum of its proper divisors (1).

78391309 is an equidigital number, since it uses as much as digits as its factorization.

78391309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 40824, while the sum is 40.

The square root of 78391309 is about 8853.8866606706. The cubic root of 78391309 is about 427.9791765715.

The spelling of 78391309 in words is "seventy-eight million, three hundred ninety-one thousand, three hundred nine".