a(n) = Sum_{k=0..n} binomial(7*n+1,7*k).A387816a(n) = Sum_{k=0..n} binomial(7*n+1,7*k).Terms a(0) =1a(1) =9a(2) =6451a(3) =490337a(4) =83411715a(5) =9402807817External referencesoeis: A387816