I’ve come across various problems where we need to present a solution modulus 1000000007 (**M**). Most of these problems involve calculating permutations and combinations involving *big numbers*. One such problem is **MOVES** The solution is presented here.

In this solution (and many others where we need to calculate permutations and combinations), a

factorial lookup table has been constructed. In addition to this, there’s another table which carries the lookup values of factorial of a number in denominator. e.g. for C(n,r) = n!/((n-r!)r!), two tables are used - fact and inverseFact. So C(n,r) is just a lookup == fact(n) x (inverseFact(n-r)%**M**) x (inverseFact®%**M**)

How is this inverseFact - (1/(N!)%**M**) lookup table constructed ? IT would be great in case any one can point me to the actual theory behind this.