A094793 a(n) = (1/n!)*A001688(n).

9, 53, 181, 465, 1001, 1909, 3333, 5441, 8425, 12501, 17909, 24913, 33801, 44885, 58501, 75009, 94793, 118261, 145845, 178001, 215209, 257973, 306821, 362305, 425001, 495509, 574453, 662481, 760265, 868501, 987909, 1119233, 1263241

Offset

0,1

Comments

Number of injections from {1,2,3,4} to {1,2,...,n} with no fixed points. - Fiona T. Brunk (fbrunk(AT)mcs.st-and.ac.uk), May 23 2006

In general (cf. A094792, A094794, A094795, etc.), the number of injections [k] -> [n] with no fixed points is given by Sum_{i=0..k} (-1)^i*binomial(k,i)*(n-i)!/(n-k)!, which is equal to (1/n!)*f_k(n) where f_k(n) gives the k-th differences of factorial numbers. - Fiona T. Brunk (fbrunk(AT)mcs.st-and.ac.uk), May 23 2006

Links

Table of n, a(n) for n=0..32.

Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1).

Formula

a(n) = n^4 + 6*n^3 + 17*n^2 + 20*n + 9.

a(n) = Sum_{i=0..4} (-1)^i*binomial(4,i)*(n-i)!/(n-4)!. - Fiona T. Brunk (fbrunk(AT)mcs.st-and.ac.uk), May 23 2006

G.f.: -(x^4+6*x^2+8*x+9) / (x-1)^5. - Colin Barker, Jun 16 2013

a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5). - Fung Lam, Apr 17 2014

P-recursive: n*a(n) = (n+5)*a(n-1) - a(n-2) with a(0) = 9 and a(1) = 53. Cf. A094791. - Peter Bala, Jul 25 2021

Mathematica

LinearRecurrence[{5, -10, 10, -5, 1}, {9, 53, 181, 465, 1001}, 40] (* Harvey P. Dale, May 23 2016 *)

Crossrefs

Cf. A001563, A001564, A001565, A001688, A001689, A023043.

Cf. A094791, A094792, A094794, A094795.

Sequence in context: A279358 A344820 A156544 * A197499 A036425 A126085

Adjacent sequences: A094790 A094791 A094792 * A094794 A094795 A094796

Keyword

nonn,easy

Author

Benoit Cloitre, Jun 11 2004

Status

approved