4,15,30,49,72... nth... Find the nth term and the 100th term of the sequence.

If you look at the difference between the first two numbers (4 and 15), you'll see it's 11. The next two (15 and 30), differ by 15. The next two differ by 19, then 23, etc. Notice that the difference increases by 4 each time.

That works out so that the nth term = 2n(n+1)+3n-3 or 2n^2 + 5n - 3. So the 100th term is 100^2 + 5*100 -3 = 10000 + 500 - 3 = 10497.

Thank you, I couldn't have even come close.

Using the formula that jcaron2 supplied, the 100th term is actually 2*100^2 + 5*100 -3 = 20,497.

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Originally Posted by ebaines

Using the formula that jcaron2 supplied, the 100th term is actually 2*100^2 + 5*100 -3 = 20,497.

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:o

Oops.