SERIESSUMMA(x;n;m;koefficienter) = koefficient_1*x^n + koefficient_2*x^(n+m) + koefficient_3*x^(n+2m) +...+ koefficient_i*x^(n+(i-1)m)
SERIESSUM(x;n;m;coefficients) = coefficient_1*x^n + coefficient_2*x^(n+m) + coefficient_3*x^(n+2m) +...+ coefficient_i*x^(n+(i-1)m)