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Question Number 21651 by Tinkutara last updated on 30/Sep/17
$${How}\:{many}\:{four}-{digit}\:{numbers}\:{are} \\ $$$${there}\:{whose}\:{decimal}\:{notation}\:{contains} \\ $$$${not}\:{more}\:{than}\:{two}\:{distinct}\:{digits}? \\ $$
Commented by mrW1 last updated on 01/Oct/17
$$\mathrm{576}\:? \\ $$
Commented by Tinkutara last updated on 02/Oct/17
$$\mathrm{Yes}.\:\mathrm{Now}\:\mathrm{I}\:\mathrm{got}\:\mathrm{it}. \\ $$
Commented by mrW1 last updated on 05/Oct/17
$$\mathrm{see}\:\mathrm{Q21693} \\ $$$$ \\ $$$$\frac{\mathrm{9}}{\mathrm{10}}×\mathrm{C}_{\mathrm{2}} ^{\mathrm{10}} ×\mathrm{2}!×\left\{_{\mathrm{2}} ^{\mathrm{4}} \right\}+\mathrm{9}=\frac{\mathrm{9}}{\mathrm{10}}×\mathrm{45}×\mathrm{2}×\mathrm{7}+\mathrm{9} \\ $$$$=\mathrm{567}+\mathrm{9}=\mathrm{576} \\ $$
Commented by Tinkutara last updated on 05/Oct/17
$$\mathrm{Can}\:\mathrm{you}\:\mathrm{explain}\:\mathrm{what}\:\mathrm{is}\:\mathrm{stirling} \\ $$$$\mathrm{function}\:\mathrm{and}\:\mathrm{where}\:\mathrm{it}\:\mathrm{is}\:\mathrm{used}? \\ $$