Number of equilateral triangles bounded by the sides and diagonals of a regular 3n-gon.

Terms

a(0) =1a(1) =14a(2) =69a(3) =188a(4) =465a(5) =882a(6) =1645a(7) =2648a(8) =4257a(9) =6170a(10) =9141a(11) =12564a(12) =17329a(13) =22778a(14) =30045a(15) =38192a(16) =48705a(17) =60318a(18) =74917a(19) =90740a(20) =110481a(21) =131714a(22) =157389a(23) =184968a(24) =217825a(25) =252902a(26) =294165a(27) =337988a(28) =388977a(29) =442710