POTENZREIHE(X;N;M;Koeffizienten) = Koeffizient_1*X^N + Koeffizient_2*X^(N+M) + Koeffizient_3*X^(N+2M) +...+ Koeffizient_i*X^(N+(i-1)M)
SERIESSUM(x; n; m; coefficients) = coefficient_1*x^n + coefficient_2*x^(n+m) + coefficient_3*x^(n+2*m) + ... + coefficient_i*x^(n+(i-1)*m)