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 A016051 Numbers of the form 9n+3 or 9n+6. 5
 3, 6, 12, 15, 21, 24, 30, 33, 39, 42, 48, 51, 57, 60, 66, 69, 75, 78, 84, 87, 93, 96, 102, 105, 111, 114, 120, 123, 129, 132, 138, 141, 147, 150, 156, 159, 165, 168, 174, 177, 183, 186, 192, 195, 201, 204, 210, 213, 219, 222, 228, 231, 237, 240 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n+1) = a(n) + its digital root in decimal base. LINKS Index entries for linear recurrences with constant coefficients, signature (1,1,-1). FORMULA a(n) = a(n-1) + a(n-2) - a(n-3) = 9*n/2 - 9/4 - 3*(-1)^n/4. G.f: 3*x*(1+x+x^2)/((1+x)*(x-1)^2). - R. J. Mathar, Dec 16 2009 a(n) = 9*(n-1) - a(n-1) (with a(1)=3). - Vincenzo Librandi, Nov 19 2010 MATHEMATICA Select[Range[240], MatchQ[Mod[#, 9], 3|6]&] (* Jean-François Alcover, Sep 17 2013 *) CROSSREFS Equals 3*A001651. Subsequence of A145204. - Reinhard Zumkeller, Oct 04 2008 Sequence in context: A256882 A191267 A145204 * A070790 A114614 A016052 Adjacent sequences:  A016048 A016049 A016050 * A016052 A016053 A016054 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified September 30 17:12 EDT 2020. Contains 337440 sequences. (Running on oeis4.)