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A042974
n 1's followed by a 2.
8
1, 2, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1
OFFSET
1,2
COMMENTS
The number 0.121121112... is irrational. - Robert G. Wilson v, Jul 05 2000
Fixed point of the following mapping w. Suppose x(n) takes values in {1,2} and w(n)=[x(1),x(2),...,x(n)]. Next define w(n+1)=[x(1),x(2),...,x(n),x(n-1)] if x(n)=1 and w(n+1)=[x(1),x(2),...,x(n),x(n-1),x(n-1)] if x(n)=2. Then taking x(1)=1 and x(2)=2 we get w(infinity)=A042974 (i.e., x(n)=A042974(n)). - Benoit Cloitre, Jan 11 2013
LINKS
EXAMPLE
0.1211211121111211111211111121111111211111111211111111121111111111211111...
MATHEMATICA
Table[PadLeft[{2}, n, 1], {n, 2, 20}]//Flatten (* Harvey P. Dale, Sep 11 2019 *)
PROG
(PARI) {a(n) = 1 + issquare(9 + 8*n)}; /* Michael Somos, Jan 12 2000 */
(PARI) { default(realprecision, 20080); x=0; for (n=1, 20000, x=10*x + 1 + issquare(9+8*n)); x/=10^19999; for (n=1, 20000, d=floor(x); x=(x-d)*10; write("b042974.txt", n, " ", d)); } \\ Harry J. Smith, May 08 2009
(Haskell)
a042974 n = a042974_list !! (n-1)
a042974_list = 1 : 2 :
concat (zipWith replicate (tail a042974_list) a042974_list)
-- Reinhard Zumkeller, Dec 08 2011
CROSSREFS
Cf. A042975, A056030 (continued fraction).
Sequence in context: A211983 A173264 A056731 * A235757 A361690 A020906
KEYWORD
nonn,easy,cons
STATUS
approved