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v[1] = 1; v[2] = 4; for(n = 2, N, my(i = n + 1); v[i] = 4*v[i - 1] - (1 - x)*v[i - 2]); v};\nrow(n, p) = {my(c = Vecrev(p)); c};\nT(N) = {my(v = P(N)); concat(vector(#v, i, row(i - 1, v[i])))};\nT(9)","reading":{"first_row":0,"offset":0,"reversed":false,"trim_zeros":"none","regular_triangle":false}}],"derivation":{"root":"n-75ccd0453a9b6cec","steps":["x \u21a6 (1/16)x\u22121/16"],"edges":["e-791d6802d1e7f8a6"],"text":"A011973 \u2192 x \u21a6 (1/16)x\u22121/16"},"headline":"A261711: Triangle read by rows: T(n,k) is the number of words over alphabet {0,1,2,3} having exactly k occurrences of the string 01, where n>=0 and k>=0.","chain":"A011973 \u2192 x \u21a6 (1/16)x\u22121/16"}