Total number of triangles visible in a regular (2n+1)-gon with all diagonals drawn.

Terms

a(0) =1a(1) =35a(2) =287a(3) =1302a(4) =4257a(5) =11297a(6) =25935a(7) =53516a(8) =101745a(9) =181279a(10) =306383a(11) =495650a(12) =772785a(13) =1167453a(14) =1716191a(15) =2463384a(16) =3462305a(17) =4776219a(18) =6479551a(19) =8659118a(20) =11415425a(21) =14864025a(22) =19136943a(23) =24384164a(24) =30775185a(25) =38500631a(26) =47773935a(27) =58833082a(28) =71942417a(29) =87394517