ShareMyScreen/ProjectEuler/0001

For each divisor, count the number of multiples m below 1000. The sum of the integers from 1 to m is 0.5m²+0.5m. Multiply the sum by the divisor. Add the results, which will double-count the numbers that are multiples of both 3 and 5, i. e. multiples of 15. Repeat the procedure for a divisor of 15, and subtract that total. Solution:

  +/ 3 5 _15 * 0 0.5 0.5 p. <. 999 % 3 5 15

NB. slow-motion replay
   999 % 3 5 15  NB. count multiples for each divisor
333 199.8 66.6
   <. 999 % 3 5 15  NB. round down
333 199 66
   0 0.5 0.5 p. <. 999 % 3 5 15  NB. calculate sum of integers 1..m for each m
55611 19900 2211
   3 5 _15 * 0 0.5 0.5 p. <. 999 % 3 5 15   NB. multiply by m and choose sign
166847 99500 _33165
   +/ 3 5 _15 * 0 0.5 0.5 p. <. 999 % 3 5 15  NB.  final total - no spoiler!
233182