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A020906
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Triangle where nth row is the first n terms of the sequence in reverse order, starting with a(1) = 1 and a(2) = 2.
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1
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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
(list; table; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Lim f(f(...f(n))) where f(n) is fractal sequence in A004736.
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REFERENCES
| C. Kimberling, "Numeration systems and fractal sequences," Acta Arithmetica 73 (1995) 103-117.
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LINKS
| C. Kimberling, Fractal sequences
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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.
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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. */
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CROSSREFS
| Cf. A004736, A020907.
Sequence in context: A173264 A056731 A042974 * A191774 A097305 A120675
Adjacent sequences: A020903 A020904 A020905 * A020907 A020908 A020909
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KEYWORD
| nonn,tabl
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AUTHOR
| Clark Kimberling (ck6(AT)evansville.edu)
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