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 A025569 T(2n-1,n), where T is the array defined in A025564. 0
 1, 4, 22, 120, 665, 3732, 21153, 120835, 694590, 4013088, 23284424, 135580865, 791862354, 4637009300, 27215510265, 160053426720, 942939231825, 5564024727096, 32878367902380, 194530139772844, 1152303896900338, 6832908809693304, 40556775927067299, 240938382783554100 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS PROG (PARI) T(n, k) = if( k<0 || k>2*n, 0, if(n==0, 1, polcoeff( (1 + x + x^2)^n, k)+ polcoeff( (1 + x + x^2)^(n-1), k-1))); a(n) = T(2*n, n+1); \\ Michel Marcus, Sep 08 2019 CROSSREFS Cf. A025564. Sequence in context: A155596 A244900 A261193 * A098834 A065983 A236576 Adjacent sequences:  A025566 A025567 A025568 * A025570 A025571 A025572 KEYWORD nonn AUTHOR EXTENSIONS a(19) corrected and more terms from Sean A. Irvine, Sep 07 2019 STATUS approved

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Last modified April 12 19:50 EDT 2021. Contains 342932 sequences. (Running on oeis4.)