/* This program solve problem #44 from site: https://projecteuler.net Pentagon numbers. Pentagonal numbers are generated by the formula, Pn=n(3n−1)/2. The first ten pentagonal numbers are: 1, 5, 12, 22, 35, 51, 70, 92, 117, 145, ... It can be seen that P4 + P7 = 22 + 70 = 92 = P8. However, their difference, 70 − 22 = 48, is not pentagonal. Find the pair of pentagonal numbers, Pj and Pk, for which their sum and difference are pentagonal and D = |Pk − Pj| is minimised; what is the value of D? Program find pentagonal pairs and prove that they have alse pentagonal sum and difference. Text me, if you find any bugs. Good luck! */ #include using namespace std; class Pentagonal { private: int j=1, k=1, z=0, r=0; long long sum=0, dif=0; int MIN_j=0, MIN_k=0, MIN_z=0, MIN_r=0; bool FCT=true; public: // Constructor Pentagonal() step by step compare numbers // and looks if they pentagonal and fit all conditions Pentagonal() { while(FCT) { k=++j; while(--k>0) { sum=formula(j)+formula(k); dif=formula(j)-formula(k); // Obviously, index of pentagonal number equal // sum of pair will be bigger than max index = "j". z=j; // Obviously, index of pentagonal number equal // difference of numbers will be bigger than // min index = "k". r=k; if( (pentagon_chk(sum,z)) && (pentagon_chk(dif,r)) ) {MIN_j=j; MIN_k=k; MIN_z=z; MIN_r=r; FCT=false;} } } } // Method return "true" if given number is pentagonal, // return "false" if - not. bool pentagon_chk(long long X, int &z) { long long P=0; int i=z; while(P