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A007526 a(n) = n(a(n-1) + 1), a(0) = 0.
(Formerly M3505)
25
0, 1, 4, 15, 64, 325, 1956, 13699, 109600, 986409, 9864100, 108505111, 1302061344, 16926797485, 236975164804, 3554627472075, 56874039553216, 966858672404689, 17403456103284420, 330665665962403999 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Eighteenth- and nineteenth_century combinatorialists call this the number of (nonnull) "variations" of n distinct objects, namely the number of permutations of nonempty subsets of {1,...,n}. Some early references to this sequence are Izquierdo (1659), Caramuel de Lobkowitz (1670), Prestet (1675) and Bernoulli (1713). - Don Knuth, Oct 16 2001, Aug 16 2004

Stirling transform of A006252(n-1) = [0,1,1,2,4,14,38,...] is a(n-1)=[0,1,4,15,64,...]. - Michael Somos, Mar 04 2004

In particular, for n>=1 a(n) is the number of nonempty sequences with n or fewer terms, each a distinct element of {1,...,n}. - Rick L. Shepherd, Jun 08 2005

a(n) = VarScheme(1,n). See A128195 for the definition of VarScheme(k,n). - Peter Luschny, Feb 26 2007

if s(n) is a sequence of the form s(0)=x, s(n)= n(s(n-1)+k), then s(n)= n!*x + a(n)*k. - Gary Detlefs, Jun 06 2010

For n > 0: a(n) = n*A000522(n-1). - Reinhard Zumkeller, Aug 27 2013

REFERENCES

Jacob Bernoulli, Ars Conjectandi (1713), page 127.

Johannes Caramuel de Lobkowitz, Mathesis Biceps Vetus et Nova (Campania: 1670), volume 2, 942-943.

J. K. Horn, personal communication to Robert G. Wilson v.

Sebastian Izquierdo, Pharus Scientiarum (Lyon: 1659), 327-328.

Jean Prestet, Elemens des Mathematiques (1675), page 341.

J Sawada, A Williams, Successor rules for flipping pancakes and burnt pancakes, Preprint 2015; http://www.cis.uoguelph.ca/~sawada/papers/pancake_successor.pdf

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

T. D. Noe, Table of n, a(n) for n=0..100

J. L. Adams, Conceptual Blockbusting: A Guide to Better Ideas,  Freeman, San Francisco, 1974. [Annotated scans of pages 69 and 70 only]

J. Bernoulli, Wahrscheinlichkeitsrechnung (Ars conjectandi) von Jakob Bernoulli (1713) Uebers. und hrsg. von R. Haussner, Leipzig, W. Engelmann, (1899), [124] Kapitel VII. Variationen ohne Wiederholung. (Page 121).

Peter J. Freyd, Core algebra revisited, Theoretical Computer Science, 375 (2007), Issues 1-3, 193-200.

Z. Kasa and Z. Katai, Scattered subwords and composition of natural numbers, Acta Univ. Sapientiae, Informatica, 4, 2 (2012) 225-236. - From N. J. A. Sloane, Feb 21 2013

Elmar Teufl and Stephan Wagner, Enumeration problems for classes of self-similar graphs, Journal of Combinatorial Theory, Series A, Volume 114, Issue 7, October 2007, Pages 1254-1277.

FORMULA

a(n) = A000522(n) - 1.

a(n) = floor(e*n! - 1). - J. K. Horn

a(n) = Sum{r=1..n} nPr = n!*Sum(1/k!, k=0..n-1) = n(a(n-1) + 1).

E.g.f.: x*exp(x)/(1-x). - Vladeta Jovovic, Aug 25 2002

a(n) = sum(k=1, n, k!*C(n, k)). - Benoit Cloitre, Dec 06 2002

a(n) = Sum[n! / k! {k=0...n-1}]. - Ross La Haye, Sep 22 2004

a(n) = sum(k=1..n, prod(j=0..k-1, (n-j) ) ). - Joerg Arndt, Apr 24 2011

Binomial transform of n!-!n. - Paul Barry, May 12 2004

Inverse binomial transform of A066534. - Ross La Haye, Sep 16 2004

For n>0, a(n) = exp(1) * Integral_{x=0..infinity} exp(-exp(x/n)+x) dx. - Gerald McGarvey, Oct 19 2006

a(n) = int(((1+x)^n-1)*exp(-x),x,0,infinity). - Paul Barry, Feb 06 2008

a(n) = GAMMA(n+2)*(1+(-GAMMA(n+1)+exp(1)*GAMMA(n+1, 1))/GAMMA(n+1)). - Thomas Wieder, May 02 2009

E.g.f.: -1/G(0) where G(k)= 1 - 1/(x - x^3/(x^2+(k+1)/G(k+1))); (continued fraction, 3rd kind, 3-step). - Sergei N. Gladkovskii, Jun 10 2012

Conjecture: a(n) +(-n-2)*a(n-1) +(2*n-1)*a(n-2) +(-n+2)*a(n-3)=0. - R. J. Mathar, Dec 04 2012

G.f.: (Q(0) - 1)/(1-x), where Q(k)= 1 + (2*k + 1)*x/( 1 - x - 2*x*(1-x)*(k+1)/(2*x*(k+1) + (1-x)/Q(k+1))); (continued fraction). - Sergei N. Gladkovskii, May 09 2013

G.f.: 2/((1-x)*G(0)) - 1/(1-x), where G(k)= 1 + 1/(1 - x*(2*k+2)/(x*(2*k+3) - 1 + x*(2*k+2)/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, May 31 2013

a(n) = (...((((((0)+1)*1+1)*2+1)*3+1)*4+1)...*n). - Bob Selcoe, Jul 04 2013

G.f.: Q(0)/(2-2*x) - 1/(1-x), where Q(k)= 1 + 1/(1 - x*(k+1)/(x*(k+1) + (1-x)/Q(k+1) )); (continued fraction). - Sergei N. Gladkovskii, Aug 09 2013

G.f.: (W(0) - 1)/(1-x), where W(k) = 1 - x*(k+1)/( x*(k+2) - 1/(1 - x*(k+1)/( x*(k+1) - 1/W(k+1) ))); (continued fraction). - Sergei N. Gladkovskii, Aug 25 2013

a(n) = (...(((((0)*1+1)*2+2)*3+3)*4+4)...*n+n). - Bob Selcoe, Apr 30 2014

0 = 1 + a(n)*(+1 + a(n+1) - a(n+2)) + a(n+1)*(+2 +a(n+1)) - a(n+2) for all n>=0. - Michael Somos, Aug 30 2016

EXAMPLE

Consider the nonempty subsets of the set {1,2,3,...,n} formed by the first n integers. E.g., for n = 3 we have {1}, {2}, {3}, {1,2}, {1,3}, {2,3}, {1,2,3}. For each subset S we determine its number of parts, that is nprts(S). The sum over all subsets is written as sum_{S=subsets}. Then we have A0007526 = sum_{S=subsets} nprts(S)!. E.g., for n = 3 we have 1!+1!+1!+2!+2!+2!+3! = 15. - Thomas Wieder, Jun 17 2006

.

a(3)=15: Let the objects be a, b, and c. The fifteen nonempty ordered subsets are {a}, {b}, {c}, {ab}, {ba}, {ac}, {ca}, {bc}, {cb}, {abc}, {acb}, {bac}, {bca}, {cab} and {cba}.

.

G.f. = x + 4*x^2 + 15*x^3 + 64*x^4 + 325*x^5 + 1956*x^6 + 13699*x^7 + ...

MAPLE

A007526 := n->add(n!/k!, k=0..n)-1;

MATHEMATICA

Table[ Sum[n!/(n - r)!, {r, 1, n}], {n, 0, 20}] (* or *) Table[n!*Sum[1/k!, {k, 0, n - 1}], {n, 0, 20}]

a=1; Table[a=(a-1)*(n-1); Abs[a], {n, 0, 40}] (* Vladimir Joseph Stephan Orlovsky, Nov 20 2009 *)

FoldList[#1*#2 + #2 &, 0, Range[19]] (* Robert G. Wilson v, Jul 07 2012 *)

f[n_] := Floor[E*n! - 1]; f[0] = 0; Array[f, 20, 0] (* Robert G. Wilson v, Feb 06 2015 *)

a[n_] := n (a[n - 1] +1); a[0] = 0; Array[a, 20, 0] (* Robert G. Wilson v, Feb 06 2015 *)

PROG

(PARI) {a(n) = if( n<1, 0, n * (a(n-1) + 1))}; /* Michael Somos, Apr 06 2003 */

(PARI) {a(n) = if( n<0, 0, n! * polcoeff(x * exp(x + x * O(x^n)) / (1 - x), n))}; /* Michael Somos, Mar 04 2004 */

(PARI) a(n)= sum(k=1, n, prod(j=0, k-1, n-j))

(Haskell)

a007526 n = a007526_list !! n

a007526_list = 0 : zipWith (*) [1..] (map (+ 1) a007526_list)

-- Reinhard Zumkeller, Aug 27 2013

CROSSREFS

Row sums of A068424.

Partial sums of A001339.

Cf. A000522, A007526, A001339, A128195.

Sequence in context: A027216 A124541 A134597 * A233536 A097422 A102129

Adjacent sequences:  A007523 A007524 A007525 * A007527 A007528 A007529

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Robert G. Wilson v

STATUS

approved

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Last modified September 28 18:09 EDT 2016. Contains 276601 sequences.