The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A007911

(Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
Showing entries 1-10 | older changes

A007911

a(n) = (n-1)!! - (n-2)!!.
(history; published version)

#25 by Joerg Arndt at Mon Feb 19 01:50:46 EST 2024

STATUS

editing

approved

#24 by Paolo P. Lava at Sun Feb 18 14:59:48 EST 2024

MAPLE

P:=proc(n) local i, j, k, w; for i from 1 by 1 to n do k:=i; w:=i-2; while w>0 do k:=k*w; w:=w-2; od; j:=i+1; w:=i-1; while w>0 do j:=j*w; w:=w-2; od; print(j-k); od; end: P(100); # Paolo P. Lava, Jun 14 2007

STATUS

approved

editing

#23 by Charles R Greathouse IV at Thu Sep 08 08:44:35 EDT 2022

PROG

(MAGMAMagma) DoubleFactorial:=func< n | &*[n..2 by -2] >; [DoubleFactorial((n-1))-DoubleFactorial(n-2): n in [3..30]]; // Vincenzo Librandi, Aug 08 2017

Discussion

Thu Sep 08

08:44

OEIS Server: https://oeis.org/edit/global/2944

#22 by Bruno Berselli at Tue Aug 08 02:59:20 EDT 2017

STATUS

reviewed

approved

#21 by Joerg Arndt at Tue Aug 08 02:26:14 EDT 2017

STATUS

proposed

reviewed

#20 by Robert Israel at Tue Aug 08 01:26:38 EDT 2017

STATUS

editing

proposed

#19 by Robert Israel at Tue Aug 08 01:25:42 EDT 2017

FORMULA

(n-1)*a(n+2) = a(n+1) + n^2*a(n). - Robert Israel, Aug 08 2017

MAPLE

f:= gfun:-rectoproc({(-n+1)*a(2+n)+a(1+n)+n^2*a(n), a(2)=0, a(3)=1}, a(n), remember):

map(f, [$3..100]); # Robert Israel, Aug 08 2017

STATUS

proposed

editing

#18 by Vincenzo Librandi at Tue Aug 08 01:02:04 EDT 2017

STATUS

editing

proposed

#17 by Vincenzo Librandi at Tue Aug 08 01:01:48 EDT 2017

DATA

1, 1, 5, 7, 33, 57, 279, 561, 2895, 6555, 35685, 89055, 509985, 1381905, 8294895, 24137505, 151335135, 468934515, 3061162125, 10033419375, 68000295825, 234484536825, 1645756410375, 5943863027025, 43105900812975, 162446292283275, 1214871076343925, 4761954230608575

MATHEMATICA

Table[(n - 1)!! - (n - 2)!!, {n, 3, 30}] (* Vincenzo Librandi, Aug 08 2017 *)

PROG

(MAGMA) DoubleFactorial:=func< n | &*[n..2 by -2] >; [DoubleFactorial((n-1))-DoubleFactorial(n-2): n in [3..30]]; // Vincenzo Librandi, Aug 08 2017

STATUS

reviewed

editing

#16 by Michel Marcus at Tue Aug 08 00:44:02 EDT 2017

STATUS

proposed

reviewed