Co-growth function of a certain group.

Terms

a(0) =2a(1) =2a(2) =6a(3) =22a(4) =58a(5) =146a(6) =414a(7) =1206a(8) =3410a(9) =9634a(10) =27670a(11) =79926a(12) =230666a(13) =667058a(14) =1936174a(15) =5632662a(16) =16408866a(17) =47875650a(18) =139908774a(19) =409404630a(20) =1199368026a(21) =3517351890a(22) =10325547582a(23) =30339113718a(24) =89217594738a(25) =262561101282a(26) =773248631222