A274648 A variation on Recamán's sequence (A005132): a(n) is the first positive number of the form a(n-1)-n*k, k>0 not already in the sequence; and if no such number exists, then a(n) is the first number of the form a(n-1)+n*k, k>0 not already in the sequence.

0, 1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9, 24, 8, 25, 43, 5, 45, 66, 44, 67, 19, 69, 17, 71, 15, 73, 103, 72, 40, 106, 38, 108, 36, 110, 34, 112, 32, 114, 30, 116, 28, 118, 26, 120, 168, 119, 169, 16, 68, 121, 175, 65, 177, 63, 179, 61, 181, 59, 183

Offset

0,3

Comments

Is this a permutation of the natural numbers?

The inverse is: 0, 1, 4, 2, 164, 19, 3, 5, 16, 14, 12, 10, 8, 6, 8228, 28, 51, 26, 158, 24, 7, 9, 11, 13, 15, 17, 46, 90, ..., . Robert G. Wilson v, Sep 07 2016

After 3.2*10^11 terms, the smallest number which has not appeared is 154. - Benjamin Chaffin, Oct 05 2016

Links

Robert G. Wilson v, Table of n, a(n) for n = 0..10000

Index entries for sequences related to Recamán's sequence

Mathematica

f[s_List] := Block[{k = 1, l = s[[-1]], n = Length@ s}, While[ MemberQ[s, l - k*n] && l > k*n, k++]; If[l > k*n, Append[s, l - k*n], k = 1; While[ MemberQ[s, l + k*n], k++]; Append[s, l + k*n]]]; Nest[f, {0}, 60] (* Robert G. Wilson v, Sep 07 2016 *)

Crossrefs

Cf. A273148 (inverse), A005132, A274647 (another variant).

Sequence in context: A065232 A074170 A076543 * A277558 A350578 A335299

Adjacent sequences: A274645 A274646 A274647 * A274649 A274650 A274651

Keyword

nonn

Author

Max Barrentine, Aug 12 2016

Status

approved