数列なんぞ 2020/07/05

階差数列
勉強中
数式
$\sum _{k=1}^n\left(3\left(k-1\right)+2\right)\frac{1}{2}n\left(3n+1\right)$
Σ[k=1,n](2+3(k-1)) - Wolfram|Alpha
等比数列
$\sum _{k=1}^{n}23^{k-1}3^n-1$
Σ[k=1,n]2*3^(k-1) - Wolfram|Alpha