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 A239605 First column of A316273. Recurrence similar to series reversion giving Catalan numbers. 3
 1, 1, 2, 4, 10, 24, 66, 178, 508, 1464, 4320, 12886, 38992, 119030, 366740, 1138036, 3554962, 11167292, 35259290, 111825840, 356100044, 1138107490, 3649507278, 11738028470, 37857909164, 122411024822 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Setting second term in coefficients equal to -1 gives alternating powers of 2. The algorithm is as follows: Step 1. Start with a lower triangular matrix "T" with the first column equal to any number sequence. Let the columns from the second column onwards in "T" be defined by the divisor recurrence: If n >= k: Sum_{i=1..k-1} T(n-i, k-1) - T(n-i, k), otherwise T(n, k) = 0. Step 2. Downshift matrix "T" one step to get matrix "X". Step 3. Calculate matrix powers X^0, X^1, X^2, X^3, X^4, X^5, ... and multiply by coefficient list c0, c1, c2, c3, c4, c5, ... to get matrix "B": B = c0*X^0 + c1*X^1 + c2*X^2 + c3*X^3 + c4*X^4 + c5*X^5 + ... Step 4. Take first column in matrix "B" and put it into the first column of a matrix "T". Repeat steps 1 to 4 until first column in matrix "T" has converged. This sequence a(n) is the converged first column in matrix "T", when coefficients c0, c1, c2, c3, c4, c5, ... = 1,1,1,1,1,1,... From Mats Granvik, Jul 25 2014: (Start) In the program, changing the line If[n >= k, Sum[t[n - i, k - 1], {i, 1, k - 1}] - Sum[t[n - i, k], {i, 1, k - 1}], 0]; to If[n >= k, Sum[t[n - i, k - 1], {i, 1, n - 1}] - Sum[t[n - i, k], {i, 1, n - 1}], 0]; that is, summing to (n-1) instead of (k-1), gives Catalan numbers A000108 and series reversion of x/Sum[x^n, {n, 0, nn}]. (End) From Mats Granvik, Dec 30 2017, Feb 01 2018: (Start) Let x be an arbitrary real or complex number and let "coeff" in the Mathematica program be the coefficients of the series expansion of the expression: 1/(1 + x*y) + (2*x*y)/(1 + x*y) - (x*y^2)/(1 + x*y) + (x^2*y^2)/(1 + x*y) at y=0 and the output will be the series expansion of (1 + y)/(1 + (1 - x) y) at y=0. This is equivalent to setting the coefficients "coeff" in the Mathematica program equal to: coeff = Join[{1, x}, (-Sign[x]*Abs[x])^Range[10]] which gives an output "cc" that is: Join[{1}, x*(x - 1)^Range[0, Length[coeff] - 2]] for all values of "x" (with the special case 0^0=1 for x=1). (End) LINKS MATHEMATICA Clear[t, n, k, i, nn, x]; coeff = {1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1}; mp[m_, e_] := If[e == 0, IdentityMatrix@Length@m, MatrixPower[m, e]]; nn = Length[coeff]; cc = Range[nn]*0 + 1; Monitor[ Do[Clear[t]; t[n_, 1] := t[n, 1] = cc[[n]];   t[n_, k_] :=    t[n, k] =     If[n >= k,      Sum[t[n - i, k - 1], {i, 1, k - 1}] -       Sum[t[n - i, k], {i, 1, k - 1}], 0];   A4 = Table[Table[t[n, k], {k, 1, nn}], {n, 1, nn}];   A5 = A4[[1 ;; nn - 1]]; A5 = Prepend[A5, ConstantArray[0, nn]];   cc = Total[     Table[coeff[[n]]*mp[A5, n - 1][[All, 1]], {n, 1, nn}]]; , {i, 1,    nn}], i]; cc (* Mats Granvik, Aug 26 2015 *) CROSSREFS Cf. A051731, A000079. Sequence in context: A049146 A000682 A001997 * A309508 A000084 A057734 Adjacent sequences:  A239602 A239603 A239604 * A239606 A239607 A239608 KEYWORD nonn AUTHOR Mats Granvik, Mar 22 2014 STATUS approved

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Last modified November 26 05:48 EST 2022. Contains 358353 sequences. (Running on oeis4.)