

A037575


Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1,2.


2



2, 21, 212, 2122, 21221, 212212, 2122122, 21221221, 212212212, 2122122122, 21221221221, 212212212212, 2122122122122, 21221221221221, 212212212212212, 2122122122122122
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OFFSET

1,1


LINKS

Table of n, a(n) for n=1..16.
Index entries for linear recurrences with constant coefficients, signature (10,0,1,10).


FORMULA

a(n)=10*a(n1)+(1/9)*{2*(n mod 3)+8*[(n+1) mod 3]+5*[(n+2) mod 3]}, with a(0)=0 [From Paolo P. Lava, Jul 30 2009]
G.f. x*(2+x+2*x^2) / ( (x1)*(10*x1)*(1+x+x^2) ).  R. J. Mathar, Nov 21 2011


MATHEMATICA

LinearRecurrence[{10, 0, 1, 10}, {2, 21, 212, 2122}, 30] (* or *) Table[ FromDigits[ PadRight[{}, n, {2, 1, 2}]], {n, 30}] (* Harvey P. Dale, Dec 12 2014 *)


CROSSREFS

Sequence in context: A037495 A024763 A304272 * A305659 A008351 A037743
Adjacent sequences: A037572 A037573 A037574 * A037576 A037577 A037578


KEYWORD

nonn,base


AUTHOR

Clark Kimberling


STATUS

approved



