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 A026185 If n even, then 2n. If n odd, then nearest integer to 2n/3. 4
 0, 1, 4, 2, 8, 3, 12, 5, 16, 6, 20, 7, 24, 9, 28, 10, 32, 11, 36, 13, 40, 14, 44, 15, 48, 17, 52, 18, 56, 19, 60, 21, 64, 22, 68, 23, 72, 25, 76, 26, 80, 27, 84, 29, 88, 30, 92, 31, 96, 33, 100, 34, 104, 35, 108, 37, 112, 38, 116, 39, 120, 41 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS For n > 0, position of n in A026184. In other words, this is the inverse permutation to A026184. For proof, see the Reble link. Permutation of nonnegative integers: lodumo_4 of (0,1,0,2,0,3,0,1,0,2,0,3,0,1,0,2,0,3,0,1,0,2,0,3,0,1,0,2,0,3,...). - Philippe Deléham, Oct 25 2011 LINKS F. M. Dekking, Permutations of N generated by left-right filling algorithms, arXiv:2001.08915 [math.CO], 2020. Don Reble, Proof that the two definitions are the same, Feb 01 2020 Index entries for linear recurrences with constant coefficients, signature (0,1,0,0,0,1,0,-1) FORMULA a(2n)=4n; a(6n+1)=4n+1; a(6n+3)=4n+2; a(6n+5)=4n+3. G.f.: x(1+4*x+x^2+4*x^3+x^4+4*x^5+x^6)/((1+x^2+x^4)*(1-x^2)^2). - Philippe Deléham, Oct 25 2011 MATHEMATICA Table[If[EvenQ[n], 2 n, Round[2 n/3]], {n, 0, 50}] (* Vincenzo Librandi, Feb 03 2020 *) PROG (MAGMA) [IsEven(n) select 2*n else Round(2*n/3): n in [0..79] ]; // Vincenzo Librandi, Feb 03 2020 CROSSREFS Cf. A026184. Bisections: A008586, A042968. Sequence in context: A153016 A231549 A088610 * A026209 A198473 A133640 Adjacent sequences:  A026182 A026183 A026184 * A026186 A026187 A026188 KEYWORD nonn AUTHOR EXTENSIONS Edited by N. J. A. Sloane, Feb 02 2020, changing the definition to one given by Philippe Deléham, Oct 25 2011, and making the old definition a comment. Thanks to Don Reble for proving that the two definitions produce the same sequence. STATUS approved

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Last modified February 26 09:37 EST 2020. Contains 332277 sequences. (Running on oeis4.)