Self-convolution with "addition" played by bitwise XOR.

Terms

a(0) =1a(1) =0a(2) =2a(3) =6a(4) =18a(5) =50a(6) =146a(7) =426a(8) =1282a(9) =3810a(10) =11394a(11) =34082a(12) =102338a(13) =306658a(14) =919874a(15) =2759154a(16) =8276898a(17) =24828386a(18) =74484386a(19) =223444258a(20) =670326242a(21) =2010964770a(22) =6032902242a(23) =18098635298a(24) =54295809826a(25) =162887261410a(26) =488661978274