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%I #15 Mar 23 2017 06:25:10
%S 12,21,3,42,51,6,72,81,9,102,111,12,132,141,15,162,171,18,192,201,21,
%T 222,231,24,252,261,27,282,291,30,312,321,33,342,351,36,372,381,39,
%U 402,411,42,432,441,45,462,471,48,492,501,51,522,531,54,552,561
%N Smallest multiple of 3 beginning with n.
%H Vincenzo Librandi, <a href="/A082799/b082799.txt">Table of n, a(n) for n = 1..1000</a>
%H <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,2,0,0,-1).
%F From _Colin Barker_, Mar 23 2017: (Start)
%F G.f.: 3*x*(4 + 7*x + x^2 + 6*x^3 + 3*x^4) / ((1 - x)^2*(1 + x + x^2)^2).
%F a(n) = 2*a(n-3) - a(n-6) for n>6.
%F (End)
%t Table[If[Mod[n,3]==0,n,10n+3-Mod[n,3]],{n,56}] (* _Ray Chandler_, Feb 09 2014 *)
%t With[{m3=3*Range[1000]},Table[SelectFirst[m3,Take[IntegerDigits[#],Min[ IntegerLength[#],IntegerLength[n]]]==IntegerDigits[n]&],{n,60}]] (* The program uses the SelectFirst function from Mathematica version 10 *) (* _Harvey P. Dale_, Dec 23 2014 *)
%o (PARI) Vec(3*x*(4 + 7*x + x^2 + 6*x^3 + 3*x^4) / ((1 - x)^2*(1 + x + x^2)^2) + O(x^60)) \\ _Colin Barker_, Mar 23 2017
%Y Cf. A082800, A082801, A082802, A082803, A082804.
%K base,easy,nonn
%O 1,1
%A _Amarnath Murthy_, Apr 20 2003
%E Extended by _Ray Chandler_, Feb 09 2014
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