# Project Euler Problem 12 Solved

## Highly divisible triangular number

The sequence of triangle numbers is generated by adding the natural numbers. So the 7th triangle number would be 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. The first ten terms would be:

1, 3, 6, 10, 15, 21, 28, 36, 45, 55, …

Let us list the factors of the first seven triangle numbers:

1: 1
3: 1,3
6: 1,2,3,6
10: 1,2,5,10
15: 1,3,5,15
21: 1,3,7,21
28: 1,2,4,7,14,28

We can see that 28 is the first triangle number to have over five divisors.

What is the value of the first triangle number to have over five hundred divisors?

## Solution

 `````` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 `````` ``````package main import ( "fmt" "math" ) func count_divisor(num int64) int64 { var count, factor, lastFactor, exponent int64 = 1, 2, 0, 1 for factor <= num { if math.Mod(float64(num), float64(factor)) == 0 { if factor == lastFactor { exponent++ } else { count *= (exponent + 1) exponent = 1 lastFactor = factor } num /= factor } else { factor++ } } return count } func main() { var count, n int64 = 0, 1 for count < 500 { n++ count = count_divisor(n * (n + 1) / 2) } fmt.Println(n*(n+1)/2, count) } ``````

I’m the 99509th person to have solved this problem.