1972 AHSME Problems/Problem 19

Solution

We begin by evaluating the sum of the first $n$ terms of the sequence with $1$ , $2$ , and $3$ . We find that the sum of the first term of the sequence is $1$ , the sum of the first two terms is $4$ , and the sum of the first three terms $11$ . From here, we can simply guess and check the answer choices and will find that only $\boxed{D}$ works.

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1972 AHSME Problems/Problem 19

Solution