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Question Number 21651 by Tinkutara last updated on 30/Sep/17

$$Howmanyfour-digitnumbersare$$$$therewhosedecimalnotationcontains$$$$notmorethantwodistinctdigits?$$

Commented by mrW1 last updated on 01/Oct/17

$$576?$$

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

$$\mathrm{see}\mathrm{Q}21693$$$$$$$$\frac{9}{10}\times {\mathrm{C}}_2^{10}\times 2!\times \left\{{}_2^4\right\}+9=\frac{9}{10}\times 45\times 2\times 7+9$$$$=567+9=576$$

Commented by Tinkutara last updated on 05/Oct/17

$$\mathrm{Can}\mathrm{you}\mathrm{explain}\mathrm{what}\mathrm{is}\mathrm{stirling}$$$$\mathrm{function}\mathrm{and}\mathrm{where}\mathrm{it}\mathrm{is}\mathrm{used}?$$

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