moments geométrics

sum(  k^{0}x^{k} ) =( ( x^{n+1}+(-1) )/( x+(-1) ) )
sum(  k^{1}x^{k} ) =( ( (n+1)x^{n+1}+1 )/( x+(-1) ) ) + (-1)( (x^{n+2}+(-1))/(x+(-1))^{2} )