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 A000661 Shifts 2 places left under boustrophedon transform. 2
 1, 0, 1, 1, 2, 6, 17, 62, 259, 1230, 6592, 39313, 258575, 1860318, 14538245, 122670593, 1111715644, 10771412394, 111125142979, 1216309735378, 14078811306851, 171837279141312, 2205768169095338, 29707098687614285 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 REFERENCES G. W. Hill, Acta Mathematica, VIII (1886). LINKS Vaclav Kotesovec, Table of n, a(n) for n = 0..480 J. Millar, N. J. A. Sloane and N. E. Young, A new operation on sequences: the Boustrophedon on transform, J. Combin. Theory, 17A 44-54 1996 (Abstract, pdf, ps). N. J. A. Sloane, My favorite integer sequences, in Sequences and their Applications (Proceedings of SETA '98). N. J. A. Sloane, Transforms FORMULA E.g.f. satisfies: A''(x) - (sec(x)+tan(x))*A(x) = 0 [G. W. Hill, 1886]. - Sergei N. Gladkovskii, Jun 12 2015 a(n) ~ n! * c * 2^n / (n^2 * Pi^n), where c = 21.874759697041762375842937403900898702204499795794357035182354071514... . - Vaclav Kotesovec, Jun 12 2015 MATHEMATICA nmax = 30; sectan = Normal[Series[Sec[x] + Tan[x], {x, 0, nmax+1}]]; Subscript[a, 0]=1; Subscript[a, 1]=0; egf = Sum[Subscript[a, k]*x^k, {k, 0, nmax+1}]; Table[Subscript[a, k]*k!, {k, 0, nmax}] /.Solve[Take[CoefficientList[Expand[ sectan*egf - D[egf, {x, 2}]], x], nmax-1] == ConstantArray[0, nmax-1]][[1]] (* Vaclav Kotesovec, Jun 12 2015 *) CROSSREFS Sequence in context: A000687 A085827 A150035 * A150036 A150037 A150038 Adjacent sequences:  A000658 A000659 A000660 * A000662 A000663 A000664 KEYWORD nonn,eigen AUTHOR STATUS approved

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Last modified October 20 11:06 EDT 2018. Contains 316379 sequences. (Running on oeis4.)