Number of 8-hoops with n symbols and no a-rooted trees.

Terms

a(0) =1a(1) =13a(2) =141a(3) =1204a(4) =7570a(5) =36021a(6) =136948a(7) =436696a(8) =1212399a(9) =3013165a(10) =6843991a(11) =14431308a(12) =28591576a(13) =53726869a(14) =96473910a(15) =166535536a(16) =277726093a(17) =449264781a(18) =707353489a(19) =1087078180a(20) =1634675406a(21) =2410208053a(22) =3490696936a(23) =4973757384a(24) =6981792475a(25) =9666797101a(26) =13215829563a(27) =17857209916