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A006999 Partitioning integers to avoid arithmetic progressions of length 3.
(Formerly M1047)
12
0, 1, 2, 4, 7, 11, 17, 26, 40, 61, 92, 139, 209, 314, 472, 709, 1064, 1597, 2396, 3595, 5393, 8090, 12136, 18205, 27308, 40963, 61445, 92168, 138253, 207380, 311071, 466607, 699911, 1049867, 1574801, 2362202, 3543304, 5314957, 7972436 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

a(n) = A006997(3^n-1).

It appears that, aside from the first term, this is the (L)-sieve transform of A016789 ={2,5,8,11,...,3n+2....}. This has been verified up to a(30)=311071. See A152009 for the definition of the (L)-sieve transform. - John W. Layman, Nov 20 2008

REFERENCES

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

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 0..1000

Joseph Gerver, James Propp and Jamie Simpson, Greedily partitioning the natural numbers into sets free of arithmetic progressions Proc. Amer. Math. Soc. 102 (1988), no. 3, 765-772.

D. R. Hofstadter, Eta-Lore [Cached copy, with permission]

D. R. Hofstadter, Pi-Mu Sequences [Cached copy, with permission]

D. R. Hofstadter and N. J. A. Sloane, Correspondence, 1977 and 1991

James Propp and N. J. A. Sloane, Email, March 1994

FORMULA

a(n) = floor((3a(n-1)+2)/2).

a(n) = -1 + floor(c*(3/2)^n) where c=1.081513668589844877304633988599549408710737041542024954790295591585622666484989650922411026555488940... - Benoit Cloitre, Jan 10 2002

PROG

(PARI) a(n)=if(n<1, 0, floor((3*a(n-1)+2)/2))

(Haskell)

a006999 n = a006999_list !! n

a006999_list = 0 : map ((`div` 2) . (+ 2) . (* 3)) a006999_list

-- Reinhard Zumkeller, Oct 26 2011

CROSSREFS

a(n) = A061419(n) - 1 = A061418(n) - 2.

The constant c is 2/3*K(3) (see A083286). - Ralf Stephan, May 29 2003

Cf. A003312.

First differences are in A073941.

Cf. A016789, A152009. - John W. Layman, Nov 20 2008

Cf. A005428 (first differences).

Sequence in context: A117276 A035295 A289010 * A005252 A023430 A023429

Adjacent sequences:  A006996 A006997 A006998 * A007000 A007001 A007002

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, D. R. Hofstadter, and James Propp, Jul 15 1977

EXTENSIONS

More terms from James A. Sellers, Feb 06 2000

STATUS

approved

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Last modified May 27 09:45 EDT 2018. Contains 304690 sequences. (Running on oeis4.)