Daca x*y=x+y+1 atunci : [tex] C_{n}^0* C_{n}^1* C_{n}^2=(C_{n}^0+ C_{n}^1+1)+ [(C_{n}^0+ C_{n}^1+1)+ C_{n}^2+1]=n+6[/tex]. Valorile combinarilor sunt:
[tex] C_{n}^0=1; C_{n}^1=n; C_{n}^2= \frac{n(n+1)}{2} [/tex] din formula combinarilor, inlocuind obtinem ecuatia : [tex] n^{2}+n-2=0 [/tex], cu radacinile [tex] n_{1}=-2,si. n_{2}=1 [/tex] dar nici una nu verifica conditia n≥2, deci solutia -zero- elemente adica multimea vida
