78438991 has 2 divisors, whose sum is σ = 78438992. Its totient is φ = 78438990.

The previous prime is 78438989. The next prime is 78439019. The reversal of 78438991 is 19983487.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 78438991 - 2¹ = 78438989 is a prime.

Together with 78438989, 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 (78438491) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39219495 + 39219496.

It is an arithmetic number, because the mean of its divisors is an integer number (39219496).

Almost surely, 2^78438991 is an apocalyptic number.

78438991 is a deficient number, since it is larger than the sum of its proper divisors (1).

78438991 is an equidigital number, since it uses as much as digits as its factorization.

78438991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 435456, while the sum is 49.

The square root of 78438991 is about 8856.5789670730. The cubic root of 78438991 is about 428.0659326470.

The spelling of 78438991 in words is "seventy-eight million, four hundred thirty-eight thousand, nine hundred ninety-one".