A080725 a(1) = 2; for n>1, 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) == 1 mod 3".
2, 4, 5, 7, 10, 11, 13, 14, 15, 16, 19, 20, 22, 25, 28, 31, 32, 33, 34, 37, 38, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 52, 55, 58, 59, 60, 61, 64, 65, 67, 70, 73, 76, 79, 82, 85, 88, 91, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 106, 109, 112, 113, 114, 115, 118, 119, 121
Offset: 1
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
Programs
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PARI
{a=2; m=[2]; for(n=2,68,print1(a,","); a=a+1; if(m[1]==n, while(a%3!=1,a++); m=if(length(m)==1,[],vecextract(m,"2..")),if(a%3==1,a++)); m=concat(m,a))}
Formula
a(a(n)) = 3*n+1, n >= 1.
Extensions
More terms and PARI code from Klaus Brockhaus, Mar 08 2003