Modified variant of A006645, the self-convolution of the Pell series.

Terms

a(0) =1a(1) =2a(2) =8a(3) =22a(4) =68a(5) =188a(6) =532a(7) =1444a(8) =3921a(9) =10446a(10) =27704a(11) =72714a(12) =189912a(13) =492760a(14) =1273064a(15) =3273896a(16) =8389489a(17) =21423994a(18) =54550728a(19) =138520286a(20) =350899964a(21) =886925652a(22) =2237284668a(23) =5633150988a(24) =14159465505a(25) =35535456518a(26) =89053087224a(27) =222870328210a(28) =557074041840