A080711 a(0) = 2; 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".

2, 4, 6, 7, 9, 10, 12, 15, 16, 18, 21, 22, 24, 25, 26, 27, 30, 31, 33, 34, 35, 36, 39, 40, 42, 45, 48, 51, 52, 53, 54, 57, 58, 60, 63, 66, 69, 70, 71, 72, 75, 76, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 90, 93, 96, 97, 98, 99, 102, 103, 105, 106, 107, 108, 109, 110, 111, 112

Offset: 0

Author

N. J. A. Sloane, Mar 05 2003

Keywords

• nonn
• easy

Links

• B. Cloitre, N. J. A. Sloane and M. J. Vandermast, Numerical analogues of Aronson's sequence, J. Integer Seqs., Vol. 6 (2003), #03.2.2.
• B. Cloitre, N. J. A. Sloane and M. J. Vandermast, Numerical analogues of Aronson's sequence (math.NT/0305308)
• Index entries for sequences of the a(a(n)) = 2n family

Crossrefs

Cf. A079000, A003605, A079253, A080710, A080712.

Programs

PARI

{a=2; m=[2]; for(n=1,68,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))}

Formula

a(a(n)) = 3*(n+2).

Extensions

More terms and PARI code from Klaus Brockhaus, Mar 06 2003