Square root of floor(A055851(n)/6).

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =2a(5) =4a(6) =11a(7) =20a(8) =40a(9) =109a(10) =198a(11) =396a(12) =1079a(13) =1960a(14) =3920a(15) =10681a(16) =19402a(17) =38804a(18) =105731a(19) =192060a(20) =384120a(21) =1046629a(22) =1901198a(23) =3802396a(24) =10360559a(25) =18819920a(26) =37639840a(27) =102558961a(28) =186298002