Question Number 166043 by mkam last updated on 12/Feb/22
$$\boldsymbol{{is}}\:\mathrm{811}\:\boldsymbol{{prime}}\:\boldsymbol{{number}}\:\boldsymbol{{or}}\:\boldsymbol{{no}}\:? \\ $$
Commented by mahdipoor last updated on 12/Feb/22
$${yes} \\ $$
Commented by mkam last updated on 12/Feb/22
$${how}\:{can}\:{you}\:{prove}\:{this} \\ $$
Commented by MJS_new last updated on 12/Feb/22
$$\mathrm{try}\:\mathrm{to}\:\mathrm{divide}\:\mathrm{by}\:\mathrm{all}\:\mathrm{prime}\:\mathrm{numbers}\:\leqslant\sqrt{\mathrm{811}} \\ $$$$\sqrt{\mathrm{811}}=\mathrm{28}.\mathrm{47}...\:\Rightarrow\:\mathrm{you}\:\mathrm{must}\:\mathrm{try} \\ $$$$\mathrm{2},\:\mathrm{3},\:\mathrm{5},\:\mathrm{7},\:\mathrm{11},\:\mathrm{13},\:\mathrm{17},\:\mathrm{19},\:\mathrm{23} \\ $$
Commented by alephzero last updated on 20/Feb/22
$$\sqrt{\mathrm{811}}\:\approx\:\mathrm{28} \\ $$$$\Rightarrow\:\mathrm{2}\nmid\mathrm{811},\:\mathrm{3}\nmid\mathrm{811},\:\mathrm{5}\nmid\mathrm{811},\:\mathrm{7}\nmid\mathrm{811}, \\ $$$$\mathrm{11}\nmid\mathrm{811},\:\mathrm{13}\nmid\mathrm{811},\:\mathrm{17}\nmid\mathrm{811},\:\mathrm{19}\nmid\mathrm{811}, \\ $$$$\mathrm{23}\nmid\mathrm{811} \\ $$$$\Rightarrow\:\mathrm{811}\:\mathrm{is}\:\mathrm{a}\:\mathrm{prime}\:\mathrm{number} \\ $$
Commented by naka3546 last updated on 12/Feb/22
$$\mathrm{811}\:\mathrm{n}\:\mathrm{881}\:\mathrm{are}\:\:\mathrm{prime}\:\:\mathrm{numbers}\:. \\ $$