78606991 has 4 divisors (see below), whose sum is σ = 78625800. Its totient is φ = 78588184.

The previous prime is 78606989. The next prime is 78607007. The reversal of 78606991 is 19960687.

78606991 is a nontrivial binomial coefficient, being equal to C(12539, 2).

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

It is not a de Polignac number, because 78606991 - 2¹ = 78606989 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 (78606961) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1 + ... + 12538.

It is an arithmetic number, because the mean of its divisors is an integer number (19656450).

Almost surely, 2^78606991 is an apocalyptic number.

78606991 is the 12538-th triangular number.

78606991 is the 4180-th centered nonagonal number.

78606991 is a deficient number, since it is larger than the sum of its proper divisors (18809).

78606991 is a wasteful number, since it uses less digits than its factorization.

78606991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18808.

The product of its (nonzero) digits is 163296, while the sum is 46.

The square root of 78606991 is about 8866.0583688582. The cubic root of 78606991 is about 428.3713241128.

It can be divided in two parts, 78606 and 991, that added together give a palindrome (79597).

The spelling of 78606991 in words is "seventy-eight million, six hundred six thousand, nine hundred ninety-one".