Question Number 475 by 123456 last updated on 25/Jan/15 | ||
$${proof}\:{or}\:{given}\:{a}\:{counter}\:{example}: \\ $$ $${if}\:{p}\:{is}\:{prime}\:{and}\:{n}\in\mathbb{N},\mathrm{1}<{n}\leqslant{p} \\ $$ $${then}\:{pn}−\mathrm{1}\:{is}\:{prime} \\ $$ | ||
Answered by prakash jain last updated on 11/Jan/15 | ||
$${p}=\mathrm{5} \\ $$ $${n}=\mathrm{2} \\ $$ $${pn}−\mathrm{1}=\mathrm{9} \\ $$ $${p}\:\mathrm{is}\:\mathrm{prime}. \\ $$ $${pn}−\mathrm{1}=\mathrm{9}\:\mathrm{is}\:\mathrm{not}\:\mathrm{a}\:\mathrm{prime}. \\ $$ | ||