LagrangeBasic[k_,list_,x_]:=(res=1;Do[If[i≠k,res*=(x-list[[i+1]])/(list[[k+1]]-list[[i+1]])],{i,0,Length[list]-1}];Expand[res])

LagrangePolynomial[nodes_,values_,x_]:=(resultat=0;Do[resultat+=values[[k]]*LagrangeBasic[k-1,nodes,x],{k,1,Length[nodes]}];Expand[resultat])

nodes=Table[k,{k,0,6.1,1.525}];

values={1, 0.8617, 0.7385, 0.6292, 0.5328};

p[x_]:=LagrangePolynomial[nodes,values,x];

p[3]

Plot[p[x],{x,-1.525,7.625}]