%I #4 Mar 30 2012 16:44:50
%S 0,1,1,2,3,6,10,19,35,65,121,226,421,786,1467,2738,5111,9541,17810,
%T 33247,62064,115858,216279,403741,753687,1406953,2626444,4902941,
%U 9152616,17085741,31894984
%N a(n) = [ tau*a(n-2) ] + a(n-1).
%K nonn
%O 0,4
%A _N. J. A. Sloane_.