%I A061800
%S A061800 1,0,3,4,3,6,7,6,9,10,9,12,13,12,15,16,15,18,19,18,21,22,21,24,25,24,
%T A061800 27,28,27,30,31,30,33,34,33,36,37,36,39,40,39,42,43,42,45,46,45,48,49,
%U A061800 48,51,52,51,54,55,54,57,58,57,60,61,60,63,64,63,66,67,66,69,70,69,72
%N A061800 a(n) =n + (-1)^(n mod 3).
%H A061800 Harry J. Smith, <a href="b061800.txt">Table of n, a(n) for n=0,...,1000</
               a>
%F A061800 O.g.f.: (1-x+3*x^2)/[(-1+x)^2*(1+x+x^2)]. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), 
               Apr 02 2008
%e A061800 a(4) = 4 + (-1)^1 = 3
%o A061800 (PARI) { for (n=0, 1000, write("b061800.txt", n, " ", n + (-1)^(n%3)) 
               ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Jul 28 2009]
%Y A061800 Cf. A004442, A014681.
%Y A061800 Sequence in context: A074372 A049276 A101684 this_sequence A048250 A073181 
               A046897
%Y A061800 Adjacent sequences: A061797 A061798 A061799 this_sequence A061801 A061802 
               A061803
%K A061800 easy,nonn
%O A061800 0,3
%A A061800 Olivier Gerard (olivier.gerard(AT)gmail.com), Jun 22 2001