Do you mean 6C2? This is a combination symbol not a permutation. It means the number of ways of combining 2 objects out of 6 different objects=6*5/2=15. 6P2 means the number of permutations of 2 out of 6, where order is important. For example, the letters A to F. There are 6*5= 30 permutations of the letters where AB, for example, is seen to be different to BA; but there are only 15 combinations because AB is the same combination as BA. The combination function is often represented by nCR and the permutation function by nPr, meaning r ways out of N.