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A137235 a(n) = (n+1)/2 if n is odd; a(n) = n/2 + 6 if n is even. 1
6, 1, 7, 2, 8, 3, 9, 4, 10, 5, 11, 6, 12, 7, 13, 8, 14, 9, 15, 10, 16, 11, 17, 12, 18, 13, 19, 14, 20, 15, 21, 16, 22, 17, 23, 18, 24, 19, 25, 20, 26, 21, 27, 22, 28, 23, 29, 24, 30, 25, 31, 26, 32, 27, 33, 28, 34, 29, 35, 30, 36, 31, 37, 32, 38, 33, 39, 34, 40, 35, 41, 36, 42, 37 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

See the paper by A. Karabegov and J. Holland for details.

LINKS

Table of n, a(n) for n=0..73.

A. Karabegov and J. Holland, Finding all solutions to the Magic Hexagram, The College Mathematics Journal, vol. 39 (2008), pp. 102-106.

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

FORMULA

O.g.f.: -(-6+5*x)/((-1+x)^2 *(1+x)). - R. J. Mathar, Mar 16 2008

a(n) = 1/4*(2*(n + 1) - 11*(-1)^(n + 1) + 11). - Ilya Gutkovskiy, Sep 18 2015

EXAMPLE

0 is even so a(0) = 0/2 + 6 = 6.

1 is odd so a(1) = (1+1)/2 = 1.

2 is even so a(2) = 2/2 + 6 = 7.

MAPLE

A137235 := proc(n) if n mod 2 = 0 then n/2+6 ; else (n+1)/2 ; fi ; end: seq(A137235(n), n=0..80) ; # R. J. Mathar, Mar 16 2008

MATHEMATICA

Table[If[OddQ[n], (n + 1)/2, (n + 12)/2], {n, 0, 60}] (* Erich Friedman, Mar 22 2008 *)

a=5; Table[a=n-a, {n, a, 200}] (* Vladimir Joseph Stephan Orlovsky, Nov 22 2009 *)

PROG

(PARI) a(n)=(2*n+2-11*(-1)^(n+1)+11)/4 \\ Charles R Greathouse IV, Sep 18 2015

CROSSREFS

Sequence in context: A113811 A126168 A028323 * A021166 A131231 A200307

Adjacent sequences:  A137232 A137233 A137234 * A137236 A137237 A137238

KEYWORD

nonn,easy

AUTHOR

Parthasarathy Nambi, Mar 08 2008

EXTENSIONS

More terms from R. J. Mathar and Erich Friedman, Mar 22 2008, Mar 16 2008

Examples edited by Jon E. Schoenfield, Jan 26 2015

STATUS

approved

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Last modified July 22 14:46 EDT 2019. Contains 325224 sequences. (Running on oeis4.)