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 Question from Darrin, a parent: I was given a number sequence and can't figure out the next terms to this 2,9,20,35,66,91...... Every formula I work out says 54 should be after 35, not 66 Any help is greatly appreciated.

Darrin,

2,9,20,35,66,91...... = 2x1, 3x3, 4x5, 5x7, 6x11, 7x13, so I might suggest 8x17 as the next number since the first number in each product is consecutive and the second number is odd and has no proper divisors other than 1 (in fact after 1, they are primes). Now this is a suggestion and a is correct solution to your problem but the are infinitely many correct possibilities and that is the difficulty with such questions. These questions are really asking "what is the most obvious solution"; as I've said we can give many perfectly logical 'correct' answers and maybe I've given the answer they were expecting.

Penny

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