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 A037567 Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,2,1. 1
 2, 22, 221, 2212, 22122, 221221, 2212212, 22122122, 221221221, 2212212212, 22122122122, 221221221221, 2212212212212, 22122122122122, 221221221221221, 2212212212212212 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Edward Jiang, Table of n, a(n) for n = 1..1000 Index entries for linear recurrences with constant coefficients, signature (10,0,1,-10) FORMULA a(n) = 10*a(n-1)+(1/9)*{8*(n mod 3)+5*[(n+1) mod 3]+2*[(n+2) mod 3]}, with a(0)=0. [Paolo P. Lava, Jul 30 2009] G.f. x*(2+2*x+x^2) / ( (x-1)*(10*x-1)*(1+x+x^2) ). - R. J. Mathar, Nov 21 2011 (Start) a(n) = floor(221/999 * 10^n). a(n) = 10*a(n-1) + 1 + (n^2 mod 3). (End) - Robert Israel, Sep 12 2014 MAPLE seq(floor(221/999*10^n), n=1..30); # Robert Israel, Sep 12 2014 PROG (PARI) a(n)=my(S=Str); for(i=0, n-1, S=concat(S, [2, 2, 1][i%3+1])); return(eval(S)) \\ Edward Jiang, Sep 11 2014 CROSSREFS Sequence in context: A308313 A304024 A239688 * A174200 A137109 A002276 Adjacent sequences:  A037564 A037565 A037566 * A037568 A037569 A037570 KEYWORD nonn,base AUTHOR STATUS approved

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Last modified January 19 17:59 EST 2020. Contains 331051 sequences. (Running on oeis4.)