Number of 4-cycles in the n-triangular honeycomb queen graph.

Terms

a(0) =0a(1) =0a(2) =15a(3) =96a(4) =330a(5) =855a(6) =1866a(7) =3624a(8) =6468a(9) =10818a(10) =17193a(11) =26208a(12) =38598a(13) =55209a(14) =77028a(15) =105168a(16) =140904a(17) =185652a(18) =241011a(19) =308736a(20) =390786a(21) =489291a(22) =606606a(23) =745272a(24) =908076a(25) =1098006a(26) =1318317a(27) =1572480a(28) =1864254a(29) =2197629