A080904 a(1)=1; for n>1, a(n)=a(n-1)-4 if n is already in the sequence, a(n)=a(n-1)+5 otherwise.

1, 6, 11, 16, 21, 17, 22, 27, 32, 37, 33, 38, 43, 48, 53, 49, 45, 50, 55, 60, 56, 52, 57, 62, 67, 72, 68, 73, 78, 83, 88, 84, 80, 85, 90, 95, 91, 87, 92, 97, 102, 107, 103, 108, 104, 109, 114, 110, 106, 102, 107, 103, 99, 104, 100, 96, 92, 97, 102, 98, 103, 99

Offset: 1

Author

Benoit Cloitre, Apr 01 2003

Keywords

• nonn

Comments

a(n)-n is eventually periodic with period 18. - Ivan Neretin, Mar 03 2016

Links

• Ivan Neretin, Table of n, a(n) for n = 1..1000
• 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, arXiv:math/0305308 [math.NT], 2003.

Crossrefs

Cf. A080578, A080900.

Programs

Mathematica

Fold[Append[#1, #1[[-1]] + If[MemberQ[#1, #2], -4, 5]] &, {1}, Range[2, 62]] (* Ivan Neretin, Mar 03 2016 *)