Can someone give some important and essential combinatorial formulas to be know at the time of attending an interview..

Combinatorial problems and programs will also be helpful.

Best answer

Consult Discrete mathematics book:

Binomial and related theorems, Sum and Product rule, Repetitions and Without repetitions (both permutation and combinations), circular ones, grouping combinations and permutations.

If you need advanced, go for Pyola, Ramsey, etc.

Pease refer Alan Tucker book : Applied Combinatorics (google books) or Scahums Series Combinatorics.

Discrete Mathematics by Kenneth Rosen and Discrete Mathematics by Goodrich, PHI Publishers are good ones to start with

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Thank you :)