Central terms of Zorach additive triangle (cf. A035312).

Terms

a(0) =1a(1) =6a(2) =23a(3) =56a(4) =168a(5) =459a(6) =1080a(7) =2400a(8) =5461a(9) =12678a(10) =28728a(11) =63336a(12) =138717a(13) =303346a(14) =663179a(15) =1438098a(16) =3062730a(17) =6450121a(18) =13583957a(19) =28627773a(20) =59954459a(21) =124413466a(22) =258510987a(23) =543867101a(24) =1152248068a(25) =2428235533a(26) =5069886692a(27) =10511339217a(28) =21696371682a(29) =44710463120