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 A165621 Riordan array (c(x^2)*(1+xc(x^2)), xc(x^2)). 1
 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 2, 3, 3, 1, 1, 5, 5, 4, 4, 1, 1, 5, 9, 9, 5, 5, 1, 1, 14, 14, 14, 14, 6, 6, 1, 1, 14, 28, 28, 20, 20, 7, 7, 1, 1, 42, 42, 48, 48, 27, 27, 8, 8, 1, 1, 42, 90, 90, 75, 75, 35, 35, 9, 9, 1, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,7 COMMENTS Inverse of A165620. Row sums are A001405(n+1). Diagonal sums are A026008. Factors as (1+xc(x^2),x)*(c(x^2),xc(x^2)). Transforms (-2)^n to a sequence with Hankel transform F(2n+1). In general, the Hankel transform of r^n by this matrix with have a Hankel transform with g.f. (1-x)/(1+(r-1)x+x^2). LINKS P. Barry, Symmetric Third-Order Recurring Sequences, Chebyshev Polynomials, and Riordan Arrays, JIS 12 (2009) 09.8.6 FORMULA Number triangle T(n,k)=sum{j=0..n, b(n-j)*sum{i=0..k, (-1)^(k-i)*C(k,i)*sum{m=0..i, C(i,m)*(C(i-m,m+k)-C(i-m,i+k+2))}}} where b(n) is the sequence beginning with 1 followed by the aerated Catalan numbers: 1,1,0,1,0,2,0,5,0,14,... EXAMPLE Triangle begins 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 2, 3, 3, 1, 1, 5, 5, 4, 4, 1, 1, 5, 9, 9, 5, 5, 1, 1, 14, 14, 14, 14, 6, 6, 1, 1, 14, 28, 28, 20, 20, 7, 7, 1, 1, 42, 42, 48, 48, 27, 27, 8, 8, 1, 1 The production array of this matrix begins 1, 1, 0, 0, 1, 1, 1, 0, 1, -1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, -1, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, -1, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 1 MATHEMATICA (* The function RiordanArray is defined in A256893. *) nmax = 10; M = PadRight[#, nmax+1]& /@ RiordanArray[(1-#)/(1-#^4)&, #/(1+#^2)&, nmax+1]; T = Inverse[M]; Table[T[[n+1, k+1]], {n, 0, nmax}, {k, 0, n}] // Flatten (* Jean-François Alcover, Jul 16 2019 *) PROG (Sage) # Algorithm of L. Seidel (1877) # Prints the first n rows of the signed version of the triangle. def Signed_A165621_triangle(n) :     D = [0]*(n+4); D[1] = 1     b = False; h = 3     for i in range(2*n) :         if b :             for k in range(h, 0, -1) : D[k] += D[k-1]             h += 1         else :             for k in range(1, h, 1) : D[k] -= D[k+1]         if b : print [D[z] for z in (2..h-2)]         b = not b Signed_A165621_triangle(11) # Peter Luschny, May 01 2012 CROSSREFS Sequence in context: A305825 A324029 A136605 * A284321 A004739 A156282 Adjacent sequences:  A165618 A165619 A165620 * A165622 A165623 A165624 KEYWORD easy,nonn,tabl AUTHOR Paul Barry, Sep 22 2009 STATUS approved

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Last modified September 15 16:33 EDT 2019. Contains 327078 sequences. (Running on oeis4.)