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A000667 Boustrophedon transform of all-1's sequence. 29
1, 2, 4, 9, 24, 77, 294, 1309, 6664, 38177, 243034, 1701909, 13001604, 107601977, 959021574, 9157981309, 93282431344, 1009552482977, 11568619292914, 139931423833509, 1781662223749884, 23819069385695177 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Fill in a triangle, like Pascal's triangle, beginning each row with a 1 and filling in rows alternately right to left and left to right.

a(n) = A227862(n, n * (n mod 2)). - Reinhard Zumkeller, Nov 01 2013

Row sums of triangle A109449. - Reinhard Zumkeller, Nov 04 2013

REFERENCES

L. Seidel, Über eine einfache Entstehungsweise der Bernoulli'schen Zahlen und einiger verwandten Reihen, Sitzungsberichte der mathematisch-physikalischen Classe der königlich bayerischen Akademie der Wissenschaften zu München, volume 7 (1877), 157-187.

LINKS

T. D. Noe, Table of n, a(n) for n=0..100

Peter Luschny, An old operation on sequences: the Seidel transform

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

Wikipedia, Boustrophedon_transform

Index entries for sequences related to boustrophedon transform

FORMULA

E.g.f.: exp(x) * (tan(x) + sec(x)).

Lim n->infinity 2*n*a(n-1)/a(n) = Pi; lim n->infinity a(n)*a(n-2)/a(n-1)^2 = 1 + 1/(n-1). - Gerald McGarvey, Aug 13 2004

a(n) = Sum_{k, k>=0} binomial(n, k)*A000111(n-k). a(2n) = A000795(n) + A009747(n), a(2n+1) = A002084(n) + A003719(n). - Philippe Deléham, Aug 28 2005

G.f.: E(0)*x/(1-x)/(1-2*x) + 1/(1-x), where E(k) = 1 - x^2*(k+1)*(k+2)/(x^2*(k+1)*(k+2) - 2*(x*(k+2)-1)*(x*(k+3)-1)/E(k+1) ); (continued fraction). - Sergei N. Gladkovskii, Jan 16 2014

a(n) ~ n! * exp(Pi/2) * 2^(n+2) / Pi^(n+1). - Vaclav Kotesovec, Jun 12 2015

EXAMPLE

...............1..............

............1..->..2..........

.........4..<-.3...<-..1......

......1..->.5..->..8...->..9..

MATHEMATICA

With[{nn=30}, CoefficientList[Series[Exp[x](Tan[x]+Sec[x]), {x, 0, nn}], x]Range[0, nn]!] (* Harvey P. Dale, Nov 28 2011 *)

t[_, 0] = 1; t[n_, k_] := t[n, k] = t[n, k-1] + t[n-1, n-k];

a[n_] := t[n, n];

Array[a, 30, 0] (* Jean-François Alcover, Feb 12 2016 *)

PROG

(Sage) # Algorithm of L. Seidel (1877)

def A000667_list(n) :

    R = []; A = {-1:0, 0:0}

    k = 0; e = 1

    for i in range(n) :

        Am = 1

        A[k + e] = 0

        e = -e

        for j in (0..i) :

            Am += A[k]

            A[k] = Am

            k += e

        # print [A[z] for z in (-i//2..i//2)]

        R.append(A[e*i//2])

    return R

A000667_list(10)  # Peter Luschny, Jun 02 2012

(Haskell)

a000667 n = if x == 1 then last xs else x

            where xs@(x:_) = a227862_row n

-- Reinhard Zumkeller, Nov 01 2013

(PARI) x='x+O('x^33); Vec(serlaplace( exp(x)*(tan(x) + 1/cos(x)) ) ) \\ Joerg Arndt, Jul 30 2016

CROSSREFS

Absolute value of pairwise sums of A009337.

Sequence in context: A005001 A091151 A093542 * A131351 A091352 A135934

Adjacent sequences:  A000664 A000665 A000666 * A000668 A000669 A000670

KEYWORD

nonn,easy,nice

AUTHOR

N. J. A. Sloane, Simon Plouffe

STATUS

approved

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Last modified June 22 12:24 EDT 2017. Contains 288613 sequences.