Task

The objective is to write a function that finds the sum of all positive multiples of 3 or 5 below n.

Show output for n = 1000.

This is is the same as Project Euler problem 1.

Extra credit: do this efficiently for n = 1e20 or higher.




/* REXX ***************************************************************
* 14.05.2013 Walter Pachl
**********************************************************************/
Say mul35()
exit
mul35:
s=0
Do i=1 To 999
  If i//3=0 | i//5=0 Then
    s=s+i
  End
Return s