## Precalculus (6th Edition) Blitzer

The value at $n=41$ of this mathematical expression, “ ${{n}^{2}}-n+41$ ” is not a prime number.
Let us consider the expression: ${{S}_{n}}$: ${{n}^{2}}-n+41$ For $n=41$, \begin{align} & {{S}_{n}}={{n}^{2}}-n+41 \\ & {{S}_{n}}=n(n-1)+41 \\ & {{S}_{n}}=(41\times 40)+41 \\ & {{S}_{41}}=(41)(40+1) \\ & {{S}_{41}}={{41}^{2}} \\ \end{align} Since, the ${{S}_{41}}$ is a perfect square; hence it is not a prime number Thus, in the figure, one can see that the domino is true until $n=40$ but after that it does not follow; the second condition of mathematical induction does not follow and hence the domino at $n=41$ does not fall, thereby breaking the sequence.