G.f. (1-x-x^3+x^4-2*x^2)/((1-2*x)*(x-1)^2*(x+1)^2). 1, 1, 2, 1, 2, 1, 2, 11, 22, 53, 106, 223, 446, 905, 1810, 3635, 7270, 14557
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