78811991 has 8 divisors (see below), whose sum is σ = 81016320. Its totient is φ = 76624632.

The previous prime is 78811987. The next prime is 78812003. The reversal of 78811991 is 19911887.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 78811991 - 2² = 78811987 is a prime.

It is a super-2 number, since 2×78811991² = 12422659850768162, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78811921) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5480 + ... + 13698.

It is an arithmetic number, because the mean of its divisors is an integer number (10127040).

Almost surely, 2^78811991 is an apocalyptic number.

78811991 is a deficient number, since it is larger than the sum of its proper divisors (2204329).

78811991 is a wasteful number, since it uses less digits than its factorization.

78811991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8485.

The product of its digits is 36288, while the sum is 44.

The square root of 78811991 is about 8877.6117847088. The cubic root of 78811991 is about 428.7433855621.

The spelling of 78811991 in words is "seventy-eight million, eight hundred eleven thousand, nine hundred ninety-one".