1,1

A set of matrices closed under exponentiation.

The powers T^k are themselves all members of the set that is counted.

(* 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[%]

Cf. A072110.

Sequence in context: A109869 A084132 A084770 this_sequence A072888 A094583 A002058

Adjacent sequences: A086240 A086241 A086242 this_sequence A086244 A086245 A086246

hard,nonn

Wouter Meeussen (wouter.meeussen(AT)pandora.be), Aug 28 2003