A000661 Shifts 2 places left under boustrophedon transform.

1, 0, 1, 1, 2, 6, 17, 62, 259, 1230, 6592, 39313, 258575, 1860318, 14538245, 122670593, 1111715644, 10771412394, 111125142979, 1216309735378, 14078811306851, 171837279141312, 2205768169095338, 29707098687614285

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 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.

Index entries for sequences related to boustrophedon transform

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: A085827 A347825 A150035 * A150036 A150037 A150038

Adjacent sequences: A000658 A000659 A000660 * A000662 A000663 A000664

Keyword

nonn,eigen

Author

N. J. A. Sloane

Status

approved