login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A049611 a(n) = T(n,2), array T as in A049600. 18
0, 1, 4, 13, 38, 104, 272, 688, 1696, 4096, 9728, 22784, 52736, 120832, 274432, 618496, 1384448, 3080192, 6815744, 15007744, 32899072, 71827456, 156237824, 338690048, 731906048, 1577058304, 3388997632, 7264534528, 15535702016 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Refer to A089378 and A075729 for the definition of hierarchies, subhierarchies and one-step transitions. - Thomas Wieder, Feb 28 2004

We may ask for the number of one-step transitions (NOOST) between all unlabeled hierarchies of n elements with the restriction that no subhierarchies are allowed. As an example, consider n = 4 and the hierarchy H1 = [[2,2]] with two elements on level 1 and two on level 2. Starting from H1 the hierarchies [[1, 3]], [[2, 1, 1]], [[1, 2, 1]] can be reached by moving one element only, but [[1, 1, 2]] cannot be reached in a one-step transitition. The solution is n = 1, NOOST = 0; n = 2, NOOST = 1; n = 3, NOOST = 4; n = 4, NOOST = 13; n = 5, NOOST = 38; n = 6, NOOST = 104; n = 7, NOOST = 272; n = 8, NOOST = 688; n = 9, NOOST = 1696. This is sequence A049611. - Thomas Wieder, Feb 28 2004

If X_1,X_2,...,X_n are 2-blocks of a (2n+2)-set X then, for n>=1, a(n+1) is the number of (n+2)-subsets of X intersecting each X_i, (i=1,2,...,n). - Milan Janjic, Nov 18 2007

In each composition (ordered partition) of the integer n, circle the first summand once, circle the second summand twice, etc. a(n) is the total number of circles in all compositions of n (that is, add k*(k+1)/2 for each composition into k parts). Note the O.g.f. is B(A(x)) where A(x)= x/(1-x) and B(x)= x/(1-x)^3.

This is the Riordan transform with the Riordan matrix A097805 (of the associated type) of the triangular number sequence A000217. See a Feb 17 2017 comment on A097805. - Wolfdieter Lang, Feb 17 2017

REFERENCES

Sergey Kitaev, JB Remmel A note on p-Ascent Sequences, Preprint, 2016, https://pure.strath.ac.uk/portal/files/46917816/Kitaev_Remmel_JC2016_a_note_on_p_ascent_sequences.pdf

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Milan Janjic, Two Enumerative Functions

M. Janjic, On a class of polynomials with integer coefficients, JIS 11 (2008) 08.5.2

M. Janjic and B. Petkovic, A Counting Function, arXiv preprint arXiv:1301.4550 [math.CO], 2013. - From N. J. A. Sloane, Feb 13 2013

S. Kitaev, J. Remmel, p-Ascent Sequences, arXiv:1503.00914 [math.CO], 2015.

Index entries for linear recurrences with constant coefficients, signature (6,-12,8).

FORMULA

G.f.: x*(1-x)^2/(1-2*x)^3.

Binomial transform of quarter squares A002620(n+1). - Paul Barry, May 27 2003

a(n) = Sum_{k=0..n} binomial(n, k)floor((k+1)^2/4). - Paul Barry, May 27 2003

a(n) = 2^(n-4)(n^2+5n+2) - 0^n/8. - Paul Barry, Jun 09 2003

a(n+2) = A001787(n+2) + A001788(n). Floretion Algebra Multiplication Program, FAMP Code: 1vessum(pos)seq[A] (= (a(n)), from 2nd term), 1vessum(neg)seq[A] and 1vessumseq[A] with A = + .5'i + .5i' + .5'ij' + .5'ki' + 2e. Sumtype is set to: default (ver. f). - Creighton Dement, Aug 02 2005

Row sums of triangle A133729 = (1, 4, 13, 38, ...). - Gary W. Adamson, Sep 21 2007

a(n) = Hyper2F1([-n+1, 3], [1], -1) for n>0. - Peter Luschny, Aug 02 2014

MATHEMATICA

CoefficientList[Series[x (1-x)^2/(1-2x)^3, {x, 0, 40}], x] (* Harvey P. Dale, Sep 24 2013 *)

PROG

(PARI) Vec(x*(1-x)^2/(1-2*x)^3+O(x^99)) \\ Charles R Greathouse IV, Jun 12 2015

CROSSREFS

a(n+1)= A055252(n, 0), n >= 0. Row sums of triangle A055249.

Cf. A001793, A058396, A075729, A089378, A133729, A000217.

Sequence in context: A277974 A089092 A181527 * A084851 A094706 A056014

Adjacent sequences:  A049608 A049609 A049610 * A049612 A049613 A049614

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified March 30 14:31 EDT 2017. Contains 284302 sequences.