Third diagonal of triangle A056242.

Terms

a(0) =1a(1) =9a(2) =41a(3) =146a(4) =456a(5) =1312a(6) =3568a(7) =9312a(8) =23552a(9) =58112a(10) =140544a(11) =334336a(12) =784384a(13) =1818624a(14) =4173824a(15) =9494528a(16) =21430272a(17) =48037888a(18) =107020288a(19) =237109248a(20) =522715136a(21) =1147142144a(22) =2507145216a(23) =5458886656a(24) =11844714496a(25) =25618808832a(26) =55247372288