The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A308521 Expansion of e.g.f. (sec(x) + tan(x))/(1 - 2*x). 1
 1, 3, 13, 80, 645, 6466, 77653, 1087414, 17400009, 313208098, 6264212481, 137813028374, 3307515383741, 85995422345522, 2407872025035597, 72236162654825222, 2311557224345919249, 78592945837626597442, 2829346052559437183353, 107515150026347498080246 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Boustrophedon transform of A000165 (double factorial of even numbers). LINKS Robert Israel, Table of n, a(n) for n = 0..403 FORMULA a(n) ~ n! * (sec(1/2) + tan(1/2)) * 2^n. - Vaclav Kotesovec, Jun 07 2019 MAPLE N:= 25: # for a(0)..a(N) S:= series((sec(x)+tan(x))/(1-2*x), x, N+1): seq(coeff(S, x, n)*n!, n=0..N); # Robert Israel, Jun 06 2019 MATHEMATICA nmax = 19; CoefficientList[Series[(Sec[x] + Tan[x])/(1 - 2 x), {x, 0, nmax}], x] Range[0, nmax]! t[n_, 0] := 2^n n!; t[n_, k_] := t[n, k] = t[n, k - 1] + t[n - 1, n - k]; a[n_] := t[n, n]; Array[a, 20, 0] CROSSREFS Cf. A000111, A000165, A230960, A231200, A296792. Sequence in context: A258377 A335636 A201795 * A183278 A331643 A074514 Adjacent sequences:  A308518 A308519 A308520 * A308522 A308523 A308524 KEYWORD nonn AUTHOR Ilya Gutkovskiy, Jun 04 2019 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 15 01:50 EDT 2021. Contains 343909 sequences. (Running on oeis4.)