G.f.: Sum_{n>=0} x^n * Product_{k=1..n} (1 + k^2*x) / (1 + x + k^2*x^2).
A209778
G.f.: Sum_{n>=0} x^n * Product_{k=1..n} (1 + k^2*x) / (1 + x + k^2*x^2).
Terms
- a(0) =1a(1) =1a(2) =1a(3) =3a(4) =5a(5) =19a(6) =49a(7) =203a(8) =733a(9) =3315a(10) =15241a(11) =76731a(12) =419973a(13) =2375027a(14) =14842721a(15) =94159595a(16) =655550445a(17) =4632480883a(18) =35405788601a(19) =276183156827
External references
- oeis: A209778