Arithmetic Sequence Crossword Puzzle

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Across
  1. 4. 3, 6, _, 12, 15
  2. 5. 21, 28, 35, _
  3. 7. _, 19, 26, 34, 41
  4. 9. 20, 40, _, 80, 100
Down
  1. 1. 3, 8, 13, _
  2. 2. 3, 12, _, 30
  3. 3. 4, 8, 12, 16, _, 24
  4. 5. 10, 20, 30, 40, _
  5. 6. 1, 6, 11, _, 21
  6. 8. 1, 3, 5, 7, 9, _