Question Number 189700 by DAVONG last updated on 20/Mar/23
Commented by Rasheed.Sindhi last updated on 21/Mar/23
$${a}=\mathrm{21} \\ $$
Commented by mehdee42 last updated on 21/Mar/23
$${it}^{,} {s}\:{wrong}\:.{because} \\ $$$$\mathrm{21}^{\mathrm{5}} \overset{\mathrm{100}} {\equiv}\mathrm{01}\Rightarrow\mathrm{21}^{\mathrm{2020}} \overset{\mathrm{100}} {\equiv}\mathrm{01}\Rightarrow\mathrm{21}^{\mathrm{2022}} \overset{\mathrm{100}} {\equiv}\mathrm{21}^{\mathrm{2}} \overset{\mathrm{100}} {\equiv}\mathrm{41} \\ $$
Answered by mehdee42 last updated on 21/Mar/23
$$\mathrm{11}^{\mathrm{2}} \overset{\mathrm{100}} {\equiv}\mathrm{21}\Rightarrow\mathrm{11}^{\mathrm{10}} \overset{\mathrm{100}} {\equiv}\mathrm{21}^{\mathrm{5}} \overset{\mathrm{100}} {\equiv}\mathrm{01} \\ $$$$\Rightarrow\mathrm{11}^{\mathrm{2020}} \overset{\mathrm{100}} {\equiv}\mathrm{01}\Rightarrow\mathrm{11}^{\mathrm{2022}} \overset{\mathrm{100}} {\equiv}\mathrm{21}\Rightarrow{a}=\mathrm{11} \\ $$
Commented by Rasheed.Sindhi last updated on 22/Mar/23
$${It}'{s}\:{a}^{\mathrm{2021}} ,\:{not}\:{a}^{\mathrm{2022}} \\ $$
Commented by Rasheed.Sindhi last updated on 22/Mar/23
$$\mathrm{21}^{\mathrm{5}} \equiv\mathrm{1}\left({mod}\:\mathrm{100}\right) \\ $$$$\mathrm{21}^{\mathrm{2020}} \equiv\mathrm{1}\left({mod}\:\mathrm{100}\right) \\ $$$$\mathrm{21}^{\mathrm{2020}} ×\mathrm{21}\equiv\mathrm{21}\left({mod}\:\mathrm{100}\right) \\ $$$$\mathrm{21}^{\mathrm{2021}} \equiv\mathrm{21}\left({mod}\:\mathrm{100}\right) \\ $$
Answered by talminator2856792 last updated on 22/Mar/23