Problem Statement

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.

Let's start with the solution:

&1-:!#v_:3%#v_     >:>#
      >+\:v >:5%#v_^
  @.$_^#! <      >   ^


&1-::3/:1+*3*2/\5/:1+*5*2/+\96+/:1+*96+*2/-.@