A080712 - OEIS

%I #13 Sep 23 2025 09:37:39

%S 4,5,7,8,9,12,13,15,18,21,22,23,24,27,28,30,31,32,33,34,35,36,39,42,

%T 45,46,47,48,51,52,54,57,60,63,66,69,72,73,74,75,76,77,78,79,80,81,84,

%U 87,90,91,92,93,96,97,99,100,101,102,103,104,105,106,107,108,109,110,111

%N a(0) = 4; for n>0, a(n) is taken to be the smallest positive integer greater than a(n-1) which is consistent with the condition "n is a member of the sequence if and only if a(n) is a multiple of 3".

%H Benoit Cloitre, N. J. A. Sloane and M. J. Vandermast, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL6/Cloitre/cloitre2.html">Numerical analogues of Aronson's sequence</a>, J. Integer Seqs., Vol. 6 (2003), #03.2.2.

%H Benoit Cloitre, N. J. A. Sloane and M. J. Vandermast, <a href="https://arxiv.org/abs/math/0305308">Numerical analogues of Aronson's sequence</a>, arXiv:math/0305308 [math.NT], 2003.

%H <a href="/index/Aa#aan">Index entries for sequences of the a(a(n)) = 2n family</a>

%F a(a(n)) = 3*(n+3).

%o (PARI) {a=4; m=[4]; for(n=1,67,print1(a,","); a=a+1; if(m[1]==n, while(a%3>0,a++); m=if(length(m)==1,[],vecextract(m,"2..")),if(a%3==0,a++)); m=concat(m,a))} \\ _Klaus Brockhaus_, Mar 06 2003

%Y Cf. A079000, A003605, A079253, A080711, A080710.

%K nonn,easy

%O 0,1

%A _N. J. A. Sloane_, Mar 05 2003

%E More terms from _Klaus Brockhaus_, Mar 06 2003