A107638 Irregular triangle read by rows: positions of 1's in the triangle generated by the morphism 1->12, 2->1.

1, 1, 1, 3, 1, 3, 4, 1, 3, 4, 1, 3, 4, 6, 1, 3, 4, 6, 1, 3, 4, 6, 8, 1, 3, 4, 6, 8, 9, 1, 3, 4, 6, 8, 9, 1, 3, 4, 6, 8, 9, 11, 1, 3, 4, 6, 8, 9, 11, 12, 1, 3, 4, 6, 8, 9, 11, 12, 1, 3, 4, 6, 8, 9, 11, 12, 14, 1, 3, 4, 6, 8, 9, 11, 12, 14, 1, 3, 4, 6, 8, 9, 11, 12, 14, 16, 1, 3, 4, 6, 8, 9, 11, 12, 14

Offset

1,4

Links

Table of n, a(n) for n=1..95.

Example

Begins:
  row triangle              positions of 1's
   1  1(2)               -> 1;
   2  12(1)              -> 1;
   3  121(12)            -> 1, 3;
   4  1211(212)          -> 1, 3, 4;
   5  12112(121)         -> 1, 3, 4;
   6  121121(2112)       -> 1, 3, 4, 6;
   7  1211212(1121)      -> 1, 3, 4, 6;
   8  12112121(12112)    -> 1, 3, 4, 6, 8;
   9  121121211(211212)  -> 1, 3, 4, 6, 8, 9;
  10  1211212112(112121) -> 1, 3, 4, 6, 8, 9;

Mathematica

s[1] = {1, 2}; s[2] = {1}; t[a_] := Flatten[s /@ a]; p[0] = {1}; p[1] = t[p[0]]; p[n_] := t[p[n - 1]]; a = Table[Flatten[Table[If[p[i][[j]] == 1, j, {}], {j, 1, i}]], {i, 1, 20}]

Crossrefs

Cf. A107604.

Sequence in context: A030708 A095709 A076152 * A245093 A104765 A308690

Adjacent sequences: A107635 A107636 A107637 * A107639 A107640 A107641

Keyword

nonn,tabf,changed

Author

Roger L. Bagula, Jun 09 2005

Extensions

Edited by Sean A. Irvine, Jun 24 2026

Status

approved