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Conjecture: -2*(n-4)*(n+4)*a(n) +(5*n^2-5*n-46)*a(n-1) +(4*n^2+n+18)*a(n-2) +(-11*n^2+24*n-16)*a(n-3) +2*(n-2)*(2*n-5)*a(n-4)=0. - R. J. Mathar, Jun 23 2013