The $\mathrm{n}^{ ext {th }}$ term of the series $1+2+4+7+11+\ldots$ is

Question

The $\mathrm{n}^{	ext {th }}$ term of the series $1+2+4+7+11+\ldots$ is

Professor PC Thomas Classes · Answer

T_n = T_1 + \sum_{k=1}^{n-1} k = 1 + \frac{(n-1)n}{2} = \frac{n^2 - n + 2}{2} \implies 	extbf{Option B}