Top-left "head" entry of the n-th power of the E8 Cartan matrix.

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =42a(5) =132a(6) =430a(7) =1444a(8) =4981a(9) =17594a(10) =63442a(11) =232828a(12) =867146a(13) =3269060a(14) =12446684a(15) =47771496a(16) =184544427a(17) =716658870a(18) =2794956099a(19) =10938266562a(20) =42930256917a(21) =168890693650a(22) =665739119129