This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A086243 #4 Mar 30 2012 18:37:43
%S A086243 2,14,68,604,4312
%N A086243 Number of invertible (-1,0,1) n X n matrices having (Tij=-Tji; i<j) such that all T^k (k= 1..12) are also (-1,0,1) invertible matrices having (Tij=-Tji; i<j).
%C A086243 A set of matrices closed under exponentiation.
%C A086243 The powers T^k are themselves all members of the set that is counted.
%t A086243 (* trimatsig[ ] : see A072110 *) n=3; it=triamatsig/@(-1+IntegerDigits[Range[0, -1+3^(n(n+1)/2)], 3, n(n+1)/2]); result[n]=Cases[it, (q_?MatrixQ)/; Det[q]=!=0 && And@@Table[Union[Flatten[{(temp=MatrixPower[q, k]), {-1, 0, 1}}]]==={-1, 0, 1} && ((1-IdentityMatrix[n])temp===-Transpose[(1-IdentityMatrix[n])temp]), {k, 12}]]; Length[%]
%Y A086243 Cf. A072110.
%K A086243 hard,nonn
%O A086243 1,1
%A A086243 _Wouter Meeussen_, Aug 28 2003