A bisection of A000960.

Terms

a(0) =3a(1) =13a(2) =27a(3) =49a(4) =79a(5) =109a(6) =147a(7) =207a(8) =253a(9) =307a(10) =387a(11) =459a(12) =529a(13) =613a(14) =709a(15) =807a(16) =927a(17) =1009a(18) =1111a(19) =1261a(20) =1359a(21) =1483a(22) =1693a(23) =1807a(24) =1933a(25) =2161a(26) =2269a(27) =2479a(28) =2703a(29) =2799