A020906 Triangle where n-th row is the first n terms of the sequence in reverse order, starting with a(1) = 1 and a(2) = 2.

1, 2, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 2, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 1, 1, 2, 1, 1

Offset

1,2

Comments

Lim f(f(...f(n))) where f(n) is fractal sequence in A004736.

Links

Table of n, a(n) for n=1..89.

Clark Kimberling, Fractal sequences

Clark Kimberling, Numeration systems and fractal sequences, Acta Arithmetica 73 (1995) 103-117.

Example

The triangle starts:
  1
  2 1
  1 2 1
  1 1 2 1
  2 1 1 2 1
  1 2 1 1 2 1
Since the sequence starts 1,2,1,1,2, row 5 is the reversal of that, 2,1,1,2,1.

Prog

(PARI) at(n)=local(r, k); r=vector(n*(n+1)\2); r[1]=r[3]=1; r[2]=2; k=4; for(i=3, n, for(j=1, i, r[k]=r[i-j+1]; k++)); r /* Generates first n>1 rows of triangle. - Franklin T. Adams-Watters, Aug 08 2011. */

Crossrefs

Cf. A004736, A020907.

Sequence in context: A042974 A235757 A361690 * A220280 A355242 A191774

Adjacent sequences: A020903 A020904 A020905 * A020907 A020908 A020909

Keyword

nonn,tabl

Author

Clark Kimberling

Status

approved