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 A007494 Numbers that are congruent to 0 or 2 mod 3. 74
 0, 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, 18, 20, 21, 23, 24, 26, 27, 29, 30, 32, 33, 35, 36, 38, 39, 41, 42, 44, 45, 47, 48, 50, 51, 53, 54, 56, 57, 59, 60, 62, 63, 65, 66, 68, 69, 71, 72, 74, 75, 77, 78, 80, 81, 83, 84, 86, 87, 89, 90, 92, 93, 95, 96, 98, 99, 101, 102, 104, 105, 107 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The map n -> a(n) (where a(n) = 3n/2 if n even or (3n+1)/2 if n odd) was studied by Mahler, in connection with "Z-numbers" and later by Flatto. One question was whether, iterating from an initial integer, one eventually encountered an iterate = 1 (mod 4). - Jeff Lagarias, Sep 23 2002 Partial sums of 0,2,1,2,1,2,1,2,1,... . - Paul Barry, Aug 18 2007 a(n) = numbers k such that antiharmonic mean of the first k positive integers is not integer. A169609(a(n-1)) = 3. See A146535 and A169609. Complement of A016777. - Jaroslav Krizek, May 28 2010 Range of A173732. - Reinhard Zumkeller, Apr 29 2012 Number of partitions of 6n into two odd parts. - Wesley Ivan Hurt, Nov 15 2014 Numbers m such that 3 divides A000217(m). - Bruno Berselli, Aug 04 2017 Maximal length of a snake like polyomino that fits in a 2 X n rectangle. - Alain Goupil, Feb 12 2020 REFERENCES L. Flatto, Z-numbers and beta-transformations, in Symbolic dynamics and its applications (New Haven, CT, 1991), 181-201, Contemp. Math., 135, Amer. Math. Soc., Providence, RI, 1992. LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..10000 INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 1002. Attila Máder, The Use of Experimental Mathematics in the Classroom, in Interesting Mathematical Problems in Sciences and Everyday Life - 2011. Kurt Mahler, An unsolved problem on the powers of 3/2, J. Austral. Math. Soc., Vol. 8 (1968), pp. 313-321. P. Sabinin and M. G. Stone, Transforming n-gons by Folding the Plane, Amer. Math. Monthly, Vol. 102, No. 7 (1995), pp. 620-627. Eric Weisstein's World of Mathematics, Folding. Robert G. Wilson v, Notes with attachment. Index entries for linear recurrences with constant coefficients, signature (1,1,-1). FORMULA a(n) = 3*n/2 if n even, otherwise (3*n+1)/2. If u(1)=0, u(n) = n + floor(u(n-1)/3), then a(n-1) = u(n). - Benoit Cloitre, Nov 26 2002 G.f.: x*(x+2)/((1-x)^2*(1+x)). - Ralf Stephan, Apr 13 2002 a(n) = 3*floor(n/2) + 2*(n mod 2) = A032766(n) + A000035(n). - Reinhard Zumkeller, Apr 04 2005 a(n) = (6*n+1)/4 - (-1)^n/4; a(n) = Sum_{k=0..n-1} (1 + (-1)^(k/2)*cos(k*Pi/2)). - Paul Barry, Aug 18 2007 A145389(a(n)) <> 1. - Reinhard Zumkeller, Oct 10 2008 a(n) = A002943(n) - A173511(n). - Reinhard Zumkeller, Feb 20 2010 a(n) = 3*n - a(n-1) - 1 (with a(0)=0). - Vincenzo Librandi, Nov 18 2010 a(n) = Sum_{k>=0} A030308(n,k)*A042950(k). - Philippe Deléham, Oct 17 2011 a(n) = n + ceiling(n/2). - Arkadiusz Wesolowski, Sep 18 2012 a(n) = 2n - floor(n/2) = floor((3n+1)/2) = n + (n + (n mod 2))/2. - Wesley Ivan Hurt, Oct 19 2013 a(n) = A000217(n+1) - A099392(n+1). - Bui Quang Tuan, Mar 27 2015 a(n) = n + floor(n/2) + (n mod 2). - Bruno Berselli, Apr 04 2016 a(n) = Sum_{i=1..n} numerator(2/i). - Wesley Ivan Hurt, Feb 26 2017 a(n) = Sum_{k=0..n-1} Sum_{i=0..k} C(i,k)+(-1)^(k-i). - Wesley Ivan Hurt, Sep 20 2017 E.g.f.: (3*exp(x)*x + sinh(x))/2. - Stefano Spezia, Feb 11 2020 Sum_{n>=1} (-1)^(n+1)/a(n) = log(3)/2 - Pi/(6*sqrt(3)). - Amiram Eldar, Dec 04 2021 MAPLE a[0]:=0:a[1]:=2:for n from 2 to 100 do a[n]:=a[n-2]+3 od: seq(a[n], n=0..71); # Zerinvary Lajos, Mar 16 2008 A007494:=n->floor((3*n+1)/2); seq(A007494(k), k=0..100); # Wesley Ivan Hurt, Sep 27 2013 MATHEMATICA Flatten[{#, #+2}&/@(3Range[0, 40])] (* Harvey P. Dale, May 15 2011 *) Table[2n - Floor[n/2], {n, 0, 100}] (* Wesley Ivan Hurt, Sep 27 2013 *) PROG (PARI) a(n)=n+(n+1)>>1 \\ Charles R Greathouse IV, Jul 25 2011 (Magma) [(6*n+1)/4-(-1)^n/4: n in [0..80]]; // Vincenzo Librandi, Aug 20 2011 (Haskell) a007494 = flip div 2 . (+ 1) . (* 3) -- Reinhard Zumkeller, Dec 12 2014 CROSSREFS Cf. A000217, A001651, A032766, A035361, A063574, A132462. Complement of A016777. Range of A002517. Cf. A274406. [Bruno Berselli, Jun 26 2016] Sequence in context: A267528 A294732 A045506 * A258575 A052490 A332076 Adjacent sequences: A007491 A007492 A007493 * A007495 A007496 A007497 KEYWORD nonn,easy,changed AUTHOR Christopher Lam Cham Kee (Topher(AT)CyberDude.Com) STATUS approved

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Last modified April 13 17:26 EDT 2024. Contains 371644 sequences. (Running on oeis4.)