Number of bracelets with 2 blue, 2 red, and n black beads.

Terms

a(0) =4a(1) =11a(2) =18a(3) =33a(4) =48a(5) =74a(6) =100a(7) =140a(8) =180a(9) =237a(10) =294a(11) =371a(12) =448a(13) =548a(14) =648a(15) =774a(16) =900a(17) =1055a(18) =1210a(19) =1397a(20) =1584a(21) =1806a(22) =2028a(23) =2288a(24) =2548a(25) =2849a(26) =3150a(27) =3495a(28) =3840a(29) =4232