a(n) = [ n/{n*sqrt(3)} ], where {x} := x - [ x ].

Terms

a(0) =1a(1) =4a(2) =15a(3) =4a(4) =7a(5) =15a(6) =56a(7) =9a(8) =15a(9) =31a(10) =209a(11) =15a(12) =25a(13) =56a(14) =15a(15) =22a(16) =38a(17) =101a(18) =20a(19) =31a(20) =56a(21) =209a(22) =27a(23) =42a(24) =82a(25) =780a(26) =35a(27) =56a(28) =126a(29) =31