A037495 Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1.

2, 21, 212, 2121, 21212, 212121, 2121212, 21212121, 212121212, 2121212121, 21212121212, 212121212121, 2121212121212, 21212121212121, 212121212121212, 2121212121212121

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (10,1,-10).

Formula

G.f.: x*(2+x) / ((x-1)*(10*x-1)*(1+x)). - R. J. Mathar, Nov 21 2011

Mathematica

Table[-(1/6)-(1/22)*(-1)^n+(7/33)*10^n, {n, 1, 20}] (* Vincenzo Librandi, Nov 23 2011 *)
Table[FromDigits[PadRight[{}, n, {2, 1}]], {n, 20}] (* Harvey P. Dale, Aug 21 2013 *)

Prog

(Magma) [-(1/6)-(1/22)*(-1)^n+(7/33)*10^n: n in [1..20]]; // Vincenzo Librandi, Nov 23 2011

Crossrefs

Sequence in context: A329318 A037559 A042349 * A024763 A304272 A037575

Adjacent sequences: A037492 A037493 A037494 * A037496 A037497 A037498

Keyword

nonn,easy,base

Author

Clark Kimberling

Status

approved