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 A121398 Main diagonal of triangle A121400; also equals the partial sums of column 0 (A121399) of the same triangle. 2
 1, 2, 5, 11, 28, 70, 184, 486, 1313, 3576, 9851, 27319, 76286, 214120, 603858, 1709719, 4857959, 13845948, 39572583, 113380652, 325576692, 936796592, 2700456452, 7797587816, 22550434989, 65308288346, 189388557677 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS FORMULA G.f. A(x) = A(x^2*G)*G*(1-x^2*G)/(1-x), where G(x) is the g.f. of the Motzkin numbers (A001006): G = (1 + x*G + x^2*G^2). PROG (PARI) {a(n)=local(F=1+x+x^2, G=serreverse(x/(F+x^2*O(x^n)))/x, H=1+x, A); for(i=0, n, H=G*subst(H, x, x^2*G)+x^2*O(x^n)); A=(x*H-y*subst(H, x, x*y))/(x*subst(F, x, y)-y); polcoeff(polcoeff(A, n, x), n, y)} CROSSREFS Cf. A121400 (triangle), A121399 (column 0), A001006 (Motzkin). Sequence in context: A257790 A174145 A124016 * A000625 A202476 A210517 Adjacent sequences:  A121395 A121396 A121397 * A121399 A121400 A121401 KEYWORD nonn AUTHOR Paul D. Hanna, Jul 27 2006 STATUS approved

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Last modified September 26 04:23 EDT 2020. Contains 337346 sequences. (Running on oeis4.)