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Total number of onto function from a set of n elements to a set of another r elements. |
Answer» `r^n--rC_1(r-1)^n-[rC_2(r-2)^n-[rC_3(r-3)^n-[` `r^n-rC_1(r-1)^n+rC_2(r-2)^n-rC_3(r-3)^n+rC_4(r-4)^2...rC_(r-1)C_(r-1)(1)^n`. |
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