How it works
This multiplication chart 1-17 draws all 289 squares, from 1 × 1 to 17 × 17, and tints the 17 row and column. 17 is prime, so none of its answers appear on a 12 by 12 chart.
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Seventeen answers no smaller chart has
A chart from 1 to 17 has 289 squares and 114 different answers. The tinted row and column bring in 17 of them, and not one appears on a 1 to 16 chart. That is what a prime does: 51, 119 and 221 each sit in 2 squares.
Work out a 17 fact in your head
Split 17 into 10 and 7. For 17 × 6, add 60 and 42 to get 102. The last digits of the row copy the 7 times table, so an answer to 17 × 8 that does not end in 6 is wrong. To test a bigger number, take 5 times its last digit from the rest. 221 gives 22 − 5 = 17, so 221 belongs in the row.
- On this 17 multiplication chart, Partly blank under Show the numbers hides 72, 145 or 217 squares. Type the answers, then press Check.
- Count a fact and its turnaround once and the chart holds 153 facts, and 153 sits in the tinted row at 17 × 9.
Questions and answers
What is the 17 times table up to 17 × 17?
17, 34, 51, 68, 85, 102, 119, 136, 153, 170, 187, 204, 221, 238, 255, 272 and 289. Each step adds 17: add 20, then take away 3.
Why are the multiples of 17 missing from a 12 by 12 chart?
Every number on a 12 by 12 chart comes from multiplying two numbers from 1 to 12. 17 is prime and larger than 12, so no such pair can make a multiple of it. 34, 51 and 85 first appear with a 17 row.
Can a multiplication chart 17 rows deep help me divide by 17?
Yes. For 204 ÷ 17, slide along the tinted row to 204, then look up to the top of that column: 12. If the number is not in the row, use the nearest smaller one: 200 ÷ 17 is 11 with 13 left over.