X(x + 3) = x^2 + 3x FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
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Let denote the <em>k</em>th term of the sequence. Then
where <em>d</em> is the common difference between consecutive terms in the sequence and <em>a</em>₁ is the first term.
The sum of the first <em>n</em> terms is
From the formula for , we get
So we have , and
so that
.
Then the <em>n</em>th term in the sequence is