Can you hack it?

Level 3

Find the 6th term in this sequence: -7, 2, 19, 44

Someone asked for the 5th number.

Sorry, 4 terms are enough to solve this.


The answer is 118.

Guiseppi Butel by Guiseppi Butel , 90, Canada

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1 solution

Guiseppi Butel
Apr 19, 2014

By finding the first differences and the second differences the function can be determined to be f(n)=4n^2 -3n -8. Substituting 6 for n we get 118

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But it can also be -7+9=2, 2+17+19, 19+25=44, so 44+33=77. The addition increases by 8 every time, i.e., 9+8=17, 17+8=25, so 25+8=33.

A-Man The General - 2 years, 2 months ago

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That was how I did it, too. And obviously got a "wrong" answer, because I didn't see tht the asker wanted the SIXTH term, not just the fifth...it pays to pay attention, which I didn't.

Ed Miles - 1 year, 3 months ago

thats the same thing ... more rigorous

Vivek Singh - 1 year, 10 months ago

129, from the summation of n^2 starting at -7. -7 + 3^2, 2 + 4^2, 19 + 5^2, 44 + 6^2, 80 + 7^2, 129 + 8^2, ... or it could also be 37146, from f(n) = |f(n - 2) * f(n- 1)| + n * 2 + 2

Marcelo Torres - 1 year ago

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