78591991 has 2 divisors, whose sum is σ = 78591992. Its totient is φ = 78591990.

The previous prime is 78591979. The next prime is 78592021. The reversal of 78591991 is 19919587.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 78591991 - 2¹¹ = 78589943 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78591971) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39295995 + 39295996.

It is an arithmetic number, because the mean of its divisors is an integer number (39295996).

Almost surely, 2^78591991 is an apocalyptic number.

78591991 is a deficient number, since it is larger than the sum of its proper divisors (1).

78591991 is an equidigital number, since it uses as much as digits as its factorization.

78591991 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 78591991 is about 8865.2124058028. The cubic root of 78591991 is about 428.3440747187.

The spelling of 78591991 in words is "seventy-eight million, five hundred ninety-one thousand, nine hundred ninety-one".