Construct triangle in which n-th row is obtained by expanding (1 + x + x^2)^n and take the next-to-central column.

A005717

Construct triangle in which n-th row is obtained by expanding (1 + x + x^2)^n and take the next-to-central column.

Terms

    a(0) =1a(1) =2a(2) =6a(3) =16a(4) =45a(5) =126a(6) =357a(7) =1016a(8) =2907a(9) =8350a(10) =24068a(11) =69576a(12) =201643a(13) =585690a(14) =1704510a(15) =4969152a(16) =14508939a(17) =42422022a(18) =124191258a(19) =363985680a(20) =1067892399a(21) =3136046298a(22) =9217554129a(23) =27114249960a(24) =79818194925a(25) =235128465026a(26) =693085098852

External references