A001846 Centered 4-dimensional orthoplex numbers (crystal ball sequence for 4-dimensional cubic lattice).

1, 9, 41, 129, 321, 681, 1289, 2241, 3649, 5641, 8361, 11969, 16641, 22569, 29961, 39041, 50049, 63241, 78889, 97281, 118721, 143529, 172041, 204609, 241601, 283401, 330409, 383041, 441729, 506921, 579081, 658689, 746241, 842249, 947241, 1061761, 1186369

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Comments

a(n) is the number of points in the Z^4 lattice that are at distance at most n from the origin in the adjacency graph. - N. J. A. Sloane, Feb 19 2013

Number of nodes of degree 8 in virtual, optimal, chordal graphs of diameter d(G)=n. - S. Bujnowski & B. Dubalski (slawb(AT)atr.bydgoszcz.pl), Mar 07 2002

If Y_i (i=1,2,3,4) are 2-blocks of an (n+4)-set X then a(n-4) is the number of 8-subsets of X intersecting each Y_i (i=1,2,3,4). - Milan Janjic, Oct 28 2007

Equals binomial transform of [1, 8, 24, 32, 16, 0, 0, 0, ...] where (1, 8, 24, 32, 16) = row 4 of the Chebyshev triangle A013609. - Gary W. Adamson, Jul 19 2008

Comment from Ben Thurston, Feb 18 2013: In the plane, if you make a picture by taking one unit step in each of the basic 8 directions from a central dot, then from each of those going one unit step in each of the eight directions, ... (see illustration), it appears that the number of dots in the picture after n steps is equal to a(n). Response from N. J. A. Sloane, Feb 19 2013: This is correct, and follows from the fact that the Z-module Z[1,i,(+-1+i)/sqrt(2)] is essentially a copy of the Z^4 lattice.

a(n) = D(4,n) where D are the Delannoy numbers (A008288). As such, a(n) gives the number of grid paths from (0,0) to (4,n) using steps that move one unit north, east, or northeast. - Jack W Grahl, Feb 15 2021

The first comment above can be re-expressed and generalized as follows: a(n) is the number of points in Z^4 that are L1 (Manhattan) distance <= n from any given point. Equivalently, due to a symmetry that is easier to see in the Delannoy numbers array (A008288), as a special case of Dmitry Zaitsev's Dec 10 2015 comment on A008288, a(n) is the number of points in Z^n that are L1 (Manhattan) distance <= 4 from any given point. - Shel Kaphan, Jan 02 2023

Examples

			a(6)=1289: (2*6^4 + 4*6^3 + 10*6^2 + 8*6 + 3) / 3 = (2592 + 864 + 360 + 48 + 3) / 3 = 3867 / 3 = 1289.
		

References

• L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 81.
• N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
• 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..1000
• D. Bump, K. Choi, P. Kurlberg, and J. Vaaler, A local Riemann hypothesis, I pages 16 and 17
• J. H. Conway and N. J. A. Sloane, Low-Dimensional Lattices VII: Coordination Sequences, Proc. Royal Soc. London, A453 (1997), 2369-2389 (pdf).
• Milan Janjic, Two Enumerative Functions. [Broken link; WayBackMachine archive]
• G. Kreweras, Sur les hiérarchies de segments, Cahiers du Bureau Universitaire de Recherche Opérationnelle, Institut de Statistique, Université de Paris, #20 (1973).
• G. Kreweras, Sur les hiérarchies de segments, Cahiers du Bureau Universitaire de Recherche Opérationnelle, Institut de Statistique, Université de Paris, #20 (1973). (Annotated scanned copy)
• Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992; arXiv:0911.4975 [math.NT], 2009.
• Simon Plouffe, 1031 Generating Functions, Appendix to Thesis, Montreal, 1992
• R. G. Stanton and D. D. Cowan, Note on a "square" functional equation, SIAM Rev., 12 (1970), 277-279.
• Ben Thurston, Illustration of the first four clusters of points in two dimensions
• Index entries for crystal ball sequences
• Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1).

Crossrefs

Cf. A005408, A001844, A001845, A001847, A059100, A013609.

First differences are A008412.

Cf. A240876.

Row/column 4 of A008288.

Programs

Maple

for n from 1 to k do eval((2*n^4+4*n^3+10*n^2+8*n+3)/3) od;
A001846:=-(z+1)**4/(z-1)**5; # conjectured (correctly) by Simon Plouffe in his 1992 dissertation

Mathematica

CoefficientList[Series[(-z^4-4 z^3-6 z^2-4 z-1)/(z-1)^5, {z, 0, 200}], z] (* Vladimir Joseph Stephan Orlovsky, Jun 19 2011 *)
Table[(((2 n + 4) n + 10) n + 8) n/3 + 1, {n, 0, 30}] (* Robert A. Russell, Jul 02 2025 *)

Formula

G.f.: (1+x)^4 /(1-x)^5.

a(n) = (2*n^4 + 4*n^3 + 10*n^2 + 8*n + 3)/3. - S. Bujnowski & B. Dubalski (slawb(AT)atr.bydgoszcz.pl), Mar 07 2002

From Jonathan Vos Post, Mar 15 2006: (Start)

a(n) = Sum_{i=0..n} A008412(i);

a(n) = Sum_{i=0..n} 8*i*(i^2 + 2)/3;

a(n) = Sum_{i=0..n} 8*i*(A059100(i))/3. (End)

a(n) = Sum_{k=0..min(4,n)} 2^k * binomial(4,k)* binomial(n,k). See Bump et al. - Tom Copeland, Sep 05 2014

E.g.f.: exp(x)*(3 + 24*x + 36*x^2 + 16*x^3 + 2*x^4)/3. - Stefano Spezia, Mar 14 2024

Sum_{n >= 1} (-1)^(n+1)/(n*a(n-1)*a(n)) = log(2) - 7/12 = log(2) - (1 - 1/2 + 1/3 - 1/4). - Peter Bala, Mar 23 2024