G.f.: Sum_{n>=0} x^n * Sum_{k=0..n} binomial(n,k)^2 * x^k*(3-x)^(n-k).
A217617
G.f.: Sum_{n>=0} x^n * Sum_{k=0..n} binomial(n,k)^2 * x^k*(3-x)^(n-k).
Terms
- a(0) =1a(1) =3a(2) =9a(3) =33a(4) =133a(5) =549a(6) =2295a(7) =9711a(8) =41505a(9) =178749a(10) =774387a(11) =3370995a(12) =14733043a(13) =64608555a(14) =284143257a(15) =1252749777a(16) =5535201733a(17) =24503713893a(18) =108659076723a(19) =482566381299
External references
- oeis: A217617