This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A027616 Number of permutations of n elements containing a 2-cycle. 2
 0, 0, 1, 3, 9, 45, 285, 1995, 15855, 142695, 1427895, 15706845, 188471745, 2450132685, 34301992725, 514529890875, 8232476226975, 139952095858575, 2519137759913775, 47863617438361725, 957272348112505425, 20102719310362613925, 442259824841726816925, 10171975971359716789275 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 LINKS FORMULA E.g.f.: (1 - exp(-x^2/2)) / (1-x). n! * { 1 - sum[ k=0..floor(n/2) ] (-1)^k / (2^k * k!) }. a(n) + A000266(n) = n!. - Yuval Dekel (dekelyuval(AT)hotmail.com), Nov 09 2003 MATHEMATICA nn=20; Table[n!, {n, 0, nn}]-Range[0, nn]!CoefficientList[Series[Exp[-x^2/2]/(1-x), {x, 0, nn}], x]  (* Geoffrey Critzer, Oct 20 2012 *) PROG (PARI) a(n) = n! * (1 - sum(k=0, floor(n/2), (-1)^k / (2^k * k!) ) ); /* Joerg Arndt, Oct 20 2012 */ (PARI) N=33; x='x+O('x^N); v=Vec( 'a0 + serlaplace( (1-exp(-x^2/2))/(1-x) ) ); v[1]-='a0;  v /* Joerg Arndt, Oct 20 2012 */ CROSSREFS Sequence in context: A038059 A174318 A004990 * A013492 A106341 A065407 Adjacent sequences:  A027613 A027614 A027615 * A027617 A027618 A027619 KEYWORD nonn AUTHOR Joe Keane (jgk(AT)jgk.org) EXTENSIONS Added more terms, Geoffrey Critzer, Oct 20 2012 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
Recent Additions | More pages | Superseeker | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .