1,1

W. H. Press et al., Numerical Recipes, Cambridge, 1986; Chapter 11.

Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.

normalQ[a_] := Block[{b=Transpose[a]}, a.b === b.a]; cnt[n_]:= Block[{c=0, q=n^2}, Do[If[normalQ@Partition[IntegerDigits[t-1, 3, q]-1, n], c++ ], {t, 3^q}]; c]; Array[cnt, 4]; - Giovanni Resta (g.resta(AT)iit.cnr.it), Apr 03 2006

Cf. A055547, A055548.

Adjacent sequences: A055546 A055547 A055548 this_sequence A055550 A055551 A055552

Sequence in context: A124432 A126466 A002112 this_sequence A086894 A012487 A113111

nonn,more

Eric Weisstein (eric(AT)weisstein.com)

a(4) from Giovanni Resta (g.resta(AT)iit.cnr.it), Apr 03 2006