Central terms of triangle A120894 (cascadence of 1+x+x^2).

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =10a(5) =27a(6) =73a(7) =189a(8) =518a(9) =1413a(10) =3857a(11) =10707a(12) =29804a(13) =83365a(14) =234665a(15) =662654a(16) =1878059a(17) =5341302a(18) =15231940a(19) =43552610a(20) =124829236a(21) =358537455a(22) =1031835260a(23) =2974872009a(24) =8590929683a(25) =24847042484a(26) =71964879243a(27) =208704926659