Yuuki, colloquially known as Yuuki Kindergarten, is a virtual research institute.
( a + b ) n = ∑ k = 0 n ( n k ) a n − k b k {\displaystyle (a+b)^{n}=\sum _{k=0}^{n}{\binom {n}{k}}a^{n-k}b^{k}} (Binomial theorem)