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A056109 Fifth spoke of a hexagonal spiral. 42
1, 6, 17, 34, 57, 86, 121, 162, 209, 262, 321, 386, 457, 534, 617, 706, 801, 902, 1009, 1122, 1241, 1366, 1497, 1634, 1777, 1926, 2081, 2242, 2409, 2582, 2761, 2946, 3137, 3334, 3537, 3746, 3961, 4182, 4409, 4642, 4881, 5126, 5377, 5634, 5897, 6166, 6441 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Squared distance from (0,0,-1) to (n,n,n) in R^3. - James R. Buddenhagen, Jun 15 2013

LINKS

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

H. Bottomley, Illustration of initial terms

Tanya Khovanova, Recursive Sequences

G. Nebe and N. J. A. Sloane, Home page for hexagonal (or triangular) lattice A2

Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

FORMULA

a(n) = 3n^2+2n+1 = a(n-1)+6n-1 = 2a(n-1)-a(n-2)+6 = 3a(n-1)-3a(n-2)+a(n-3) = A056105(n)+4n = A056106(n)+3n = A056107(n)+2n = A056108(n)+n = A003215(n)-n.

G.f.: (1+3*x+2*x^2)/(1-3*x+3*x^2-x^3). - Colin Barker, Jan 04 2012

G.f.: (1 + x) * (1 + 2*x) / (1 - x)^3. - Michael Somos, Feb 04 2012

a(n) = A008810(3*n + 1) = A056105(-n). - Michael Somos, Aug 03 2006

MATHEMATICA

s=1; lst={s}; Do[s+=n+5; AppendTo[lst, s], {n, 0, 6!, 6}]; lst (* Vladimir Joseph Stephan Orlovsky, Nov 04 2008 *)

Table[3 n^2 + 2 n + 1, {n, 0, 100}] (* Vincenzo Librandi, Mar 15 2013 *)

PROG

(PARI) {a(n) = 3*n^2 + 2*n + 1}; /* Michael Somos, Aug 03 2006 */

(MAGMA) [3*n^2 + 2*n + 1: n in [0..50]]; // Vincenzo Librandi, Mar 15 2013

CROSSREFS

Cf. A054552 for example of square (or octagonal) spiral spoke.

Cf. A003215, A008810, A056105.

Cf. A122430 (prime terms of A056109). - Zak Seidov, Mar 13 2013

Sequence in context: A038795 A216892 A066486 * A023545 A038633 A083045

Adjacent sequences:  A056106 A056107 A056108 * A056110 A056111 A056112

KEYWORD

easy,nonn

AUTHOR

Henry Bottomley, Jun 09 2000

STATUS

approved

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Last modified March 25 15:14 EDT 2017. Contains 284082 sequences.