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%I #11 Sep 28 2022 07:53:22
%S 0,0,0,0,0,0,1,1,2,3,3,4,5,6,7,8,10,11,12,14,15,17,19,21,23,25,27,29,
%T 31,33,36,38,41,44,46,49,52,55,58,61,65,68,71,75,78,82,86,90,94,98,
%U 102,106,110,114,119,123,128,133,137,142,147,152,157,162,168,173,178,184,189
%N a(n) = floor(n*(n-1)/24).
%H <a href="/index/Rec#order_23">Index entries for linear recurrences with constant coefficients</a>, signature (2, -1, 1, -2, 1, -1, 2, -1, 1, -2, 1, -1, 2, -1, 1, -2, 1, -1, 2, -1, 1, -2, 1)
%F a(n) = +2*a(n-1) -a(n-2) +a(n-3) -2*a(n-4) +a(n-5) -a(n-6) +2*a(n-7) -a(n-8) +a(n-9) -2*a(n-10) +a(n-11) -a(n-12) +2*a(n-13) -a(n-14) +a(n-15) -2*a(n-16) +a(n-17) -a(n-18) +2*a(n-19) -a(n-20) +a(n-21) -2*a(n-22) +a(n-23). G.f.: x^6*(1-x+x^2-x^3+x^6-x^9+x^10-x^11+x^12) / ((1-x)^3*(1+x+x^2)*(x^2+1)*(x^4+1)*(x^4-x^2+1)*(x^8-x^4+1) ). [From _R. J. Mathar_, Apr 15 2010]
%t CoefficientList[Series[x^6*(1-x+x^2-x^3+x^6-x^9+x^10-x^11+x^12) / ((1-x)^3 *
%t (1+x+x^2) * (x^2+1) * (x^4+1) * (x^4-x^2+1) * (x^8-x^4+1)), {x,0,200}], x] (* _Georg Fischer_, Sep 28 2022 *)
%K nonn,easy
%O 0,9
%A _N. J. A. Sloane_.