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 A275207 Expansion of (A(x)^2+A(x^2))/2 where A(x) = A001006(x). 2
 1, 1, 3, 6, 16, 38, 100, 256, 681, 1805, 4867, 13162, 35925, 98469, 271511, 751656, 2089963, 5831451, 16326785, 45847770, 129108926, 364498596, 1031486590, 2925337352, 8313215743, 23668977163, 67507773621, 192859753310, 551821400008, 1581188102590 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Analog of A275165 with Motzkin numbers replacing connected graph counts. LINKS Alois P. Heinz, Table of n, a(n) for n = 0..1000 FORMULA a(2n+1) = A275208(2n+1). Conjecture: a(2n+1) = A026940(n+1). Conjecture D-finite with recurrence -3*(n+4)*(n+3)*(29*n-32)*a(n) +10*(29*n-40)*(n+3)*(n+2)*a(n-1) +2*(n+1)*(149*n^2 +208*n-450)*a(n-2) -2*n*(559*n^2 -381*n-1630)*a(n-3) +4*(-68*n^3 +531*n^2 -904*n+351)*a(n-4) +2*(103*n^3-1701*n^2+5330*n -3600)*a(n-5) +18*(11*n^3 -209*n^2 +834*n -778)*a(n-6) +6*n*(269*n-830)*(n-5)*a(n-7) +9*(n-5)*(n-6)*(95*n-134)*a(n-8)=0. - R. J. Mathar, Mar 07 2023 a(n) ~ 3^(n + 5/2) / (2 * sqrt(Pi) * n^(3/2)). - Vaclav Kotesovec, Mar 08 2023 MAPLE b:= proc(n) option remember; `if`(n<2, 1, ((3*(n-1))*b(n-2)+(1+2*n)*b(n-1))/(n+2)) end: a:= proc(n) option remember; add(b(j)*b(n-j), j=0..n/2)- `if`(n::odd, 0, (t-> t*(t-1)/2)(b(n/2))) end: seq(a(n), n=0..40); # Alois P. Heinz, Jul 19 2016 MATHEMATICA b[n_] := b[n] = If[n<2, 1, ((3*(n-1))*b[n-2] + (1+2*n)*b[n-1])/(n+2)]; a[n_] := a[n] = Sum[b[j]*b[n-j], {j, 0, n/2}] - If[OddQ[n], 0, Function[t, t*(t-1)/2][b[n/2]]]; Table[a[n], {n, 0, 40}] (* Jean-François Alcover, May 16 2017, after Alois P. Heinz *) CROSSREFS Cf. A275208, A026940. Sequence in context: A190735 A096588 A256943 * A073079 A143560 A279685 Adjacent sequences: A275204 A275205 A275206 * A275208 A275209 A275210 KEYWORD nonn AUTHOR R. J. Mathar, Jul 19 2016 STATUS approved

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Last modified June 23 10:38 EDT 2024. Contains 373643 sequences. (Running on oeis4.)