a(n) = floor(n*phi^4), where phi is the golden ratio, A001622.

Terms

a(0) =0a(1) =6a(2) =13a(3) =20a(4) =27a(5) =34a(6) =41a(7) =47a(8) =54a(9) =61a(10) =68a(11) =75a(12) =82a(13) =89a(14) =95a(15) =102a(16) =109a(17) =116a(18) =123a(19) =130a(20) =137a(21) =143a(22) =150a(23) =157a(24) =164a(25) =171a(26) =178a(27) =185a(28) =191a(29) =198