78195991 has 2 divisors, whose sum is σ = 78195992. Its totient is φ = 78195990.

The previous prime is 78195989. The next prime is 78196003. The reversal of 78195991 is 19959187.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 78195991 - 2¹ = 78195989 is a prime.

It is a super-2 number, since 2×78195991² = 12229226016944162, which contains 22 as substring.

Together with 78195989, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78190991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39097995 + 39097996.

It is an arithmetic number, because the mean of its divisors is an integer number (39097996).

Almost surely, 2^78195991 is an apocalyptic number.

78195991 is a deficient number, since it is larger than the sum of its proper divisors (1).

78195991 is an equidigital number, since it uses as much as digits as its factorization.

78195991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 204120, while the sum is 49.

The square root of 78195991 is about 8842.8497103592. The cubic root of 78195991 is about 427.6234332310.

The spelling of 78195991 in words is "seventy-eight million, one hundred ninety-five thousand, nine hundred ninety-one".