78505991 has 4 divisors (see below), whose sum is σ = 78831984. Its totient is φ = 78180000.

The previous prime is 78505951. The next prime is 78505993. The reversal of 78505991 is 19950587.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 78505991 - 2⁶ = 78505927 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78505993) 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 in 3 ways as a sum of consecutive naturals, for example, 162635 + ... + 163116.

It is an arithmetic number, because the mean of its divisors is an integer number (19707996).

Almost surely, 2^78505991 is an apocalyptic number.

78505991 is a deficient number, since it is larger than the sum of its proper divisors (325993).

78505991 is a wasteful number, since it uses less digits than its factorization.

78505991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 325992.

The product of its (nonzero) digits is 113400, while the sum is 44.

The square root of 78505991 is about 8860.3606585737. The cubic root of 78505991 is about 428.1877778970.

The spelling of 78505991 in words is "seventy-eight million, five hundred five thousand, nine hundred ninety-one".