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A217502 E.g.f.: exp(sec(x)-1) = 1 + sum_{n>0} a(n)*x^(2*n)/(2*n)!. 4
1, 1, 8, 151, 5123, 271396, 20605133, 2116186801, 282013329788, 47257934281891, 9716069206252163, 2402866414155189016, 703288162788887287433, 240323111593250975343601, 94776477297941909597367248, 42710529437686482677512782271 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..240

FORMULA

E.g.f.: exp(sec(x)-1) = 1 + Sum_{n>0} a(n)*x^(2*n)/(2*n)!.

a(n) = Sum_{m=1..(2*n)} (Sum_{k=m..(2*n)} binomial(k-1,m-1)*Sum_{j=(2*k)..(2*n)} binomial(j-1,2*k-1)*(j)!*2^(m-j)*(-1)^(n+k+j) * stirling2(2*n,j))))/m!), n>0, a(0)=1.

a(n) ~ 2^(4*n+1/2)* exp(4*sqrt(n)/sqrt(Pi)-2*n-1+1/Pi)* n^(2*n-1/4) / Pi^(2*n+1/4). - Vaclav Kotesovec, Sep 24 2013

a(n) = Sum_{i=0..(n-1)} binomial(2*n-1,2*i+1)*z(i)*a(n-i-1))), a(0)=1, where z(n) = euler(n+1) - secant numbers (A000364). - Vladimir Kruchinin, Mar 01 2015

MAPLE

a := proc(n) option remember; if n=0 then 1 else add((-1)^i*binomial(2*n-1, 2*i-1)* euler(2*i)*a(n-i), i=1..n) fi end: seq(a(n), n=0..15); # Peter Luschny, Mar 08 2015

MATHEMATICA

a[n_] := Sum[ (Sum[ Binomial[k - 1, m - 1]* Sum[ Binomial[j - 1, 2*k - 1]*(j)!*2^(m - j)*(-1)^(n + k + j)*StirlingS2[2*n, j], {j, 2*k, 2*n}], {k, m, 2*n}])/m!, {m, 1, 2*n}]; a[0] = 1; Table[a[n], {n, 0, 15}] (* Jean-Fran├žois Alcover, Feb 22 2013 *)

Table[(2*n)!*SeriesCoefficient[E^(1/Cos[x]-1), {x, 0, 2*n}], {n, 0, 20}] (* Vaclav Kotesovec, Sep 24 2013 *)

With[{nn = 100}, CoefficientList[Series[Exp[Sec[x] - 1], {x, 0, nn}],

x] Range[0, nn]!][[;; ;; 2]] (* G. C. Greubel, May 31 2017 *)

PROG

(Maxima) a(n):=if n=0 then 1 else sum((sum(binomial(k-1, m-1)*sum(binomial(j-1, 2*k-1)*(j)!*2^(m-j)*(-1)^(n+k+j)*stirling2(2*n, j), j, 2*k, 2*n), k, m, 2*n))/m!, m, 1, 2*n);

(Maxima)

z(n):=(2*n+2)!*(coeff(taylor(sec(x), x, 0, 20), x, 2*(n+1)));

a(n):=if n=0 then 1 else (sum(binomial(2*n-1, 2*i+1)*z(i)*a(n-i-1), i, 0, n-1)); /* Vladimir Kruchinin, Mar 01 2015 */

(PARI) a(n) = {n = 2*n+2; xx = x + O(x^n); polcoeff(serlaplace(exp(1/cos(xx)-1)), n); } \\ Michel Marcus, Mar 03 2015

CROSSREFS

Cf. A000364.

Sequence in context: A220559 A264642 A300872 * A229955 A249481 A003491

Adjacent sequences:  A217499 A217500 A217501 * A217503 A217504 A217505

KEYWORD

nonn

AUTHOR

Vladimir Kruchinin, Oct 05 2012

STATUS

approved

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Last modified January 19 12:48 EST 2020. Contains 331049 sequences. (Running on oeis4.)