Project Euler : Problem 012

Project Euler problems in Oforth . Feel free to post your own code.

Project Euler : Problem 012

Postby Franck » 01 Aug 2015 16:22

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?

Code: Select all
: nbDivisors(n)    // ( n -- n ) : Returns number of divisors of n
{
| sqrtn i |
   0 n sqrt asInteger dup ->sqrtn loop: i [ n i mod ifFalse: [ 2 + ] ]
   n sqrtn sq == -
}

: pe012(n)      // ( n -- ) : Calculate first triangle number to have over n divisors
{
| tr |
   1 ->tr
   1 while ( tr nbDivisors n < ) [ 1 + dup tr + ->tr ] drop tr
}
Franck
 
Posts: 144
Joined: 29 Oct 2014 19:01

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