A080900 a(1)=1; for n>1, a(n)=a(n-1)-2 if n is already in the sequence, a(n)=a(n-1)+5 otherwise.

1, 6, 11, 16, 21, 19, 24, 29, 34, 39, 37, 42, 47, 52, 57, 55, 60, 65, 63, 68, 66, 71, 76, 74, 79, 84, 89, 94, 92, 97, 102, 107, 112, 110, 115, 120, 118, 123, 121, 126, 131, 129, 134, 139, 144, 149, 147, 152, 157, 162, 167, 165, 170, 175, 173, 178, 176

Offset

1,2

Links

Antti Karttunen, Table of n, a(n) for n = 1..20000 (terms 1..1000 from Ivan Neretin)

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.

Formula

Perhaps this is asymptotic to c_0*n*(1 + c_1/log n + ...), with c_0 near 2 ?

Mathematica

Fold[Append[#1, #1[[-1]] + If[MemberQ[#1, #2], -2, 5]] &, {1}, Range[2, 57]] (* Ivan Neretin, Mar 03 2016 *)

Prog

(PARI)
up_to = 1001;
A080900list(up_to_n) = { my(xs=Map(), v=vector(up_to_n)); mapput(xs, 1, 1); v[1] = 1; for(n=2, up_to_n, v[n] = v[n-1]+if(mapisdefined(xs, n), -2, +5); mapput(xs, v[n], n)); (v); };
v080900 = A080900list(up_to);
A080900(n) = v080900[n]; \\ Antti Karttunen, Jan 22 2020

Crossrefs

Cf. A080912, A080913, A080904, A080914, A080578, A080919, A080922, A080927.

Cf. A080901 (starting value = 2), A080905 (run lengths of first differences).

Sequence in context: A070397 A080904 A081746 * A080783 A315457 A315458

Adjacent sequences: A080897 A080898 A080899 * A080901 A080902 A080903

Keyword

nonn

Author

N. J. A. Sloane and Benoit Cloitre, Apr 01 2003

Status

approved