IBM Ponder This #031 · November 2000

We gave you a difficult puzzle last month.
This month's will be easier.

Part A:
Select 75 integers between 1 and 230 (inclusive) such that no
two of them differ by exactly 5, 6, or 11.

Part B:
Show that one cannot select 76 integers satisfying the same requirements.

Solution

Best opened after a real attempt

To be added.