A143795 a(1) = 1, then for n > 1, a(n) = a(n - 1) + 1 for n even, or a(n) = a(n - 1) + 10 for n odd.

1, 2, 12, 13, 23, 24, 34, 35, 45, 46, 56, 57, 67, 68, 78, 79, 89, 90, 100, 101, 111, 112, 122, 123, 133, 134, 144, 145, 155, 156, 166, 167, 177, 178, 188, 189, 199, 200, 210, 211, 221, 222, 232, 233, 243, 244, 254, 255, 265, 266, 276, 277, 287, 288, 298, 299

Offset

1,2

Comments

Old name was "Start with 1; then repeatedly add 1, then add 10."

Links

Table of n, a(n) for n=1..56.

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

Formula

From R. J. Mathar, Sep 04 2008: (Start)

a(n) = (22*n - 27 - 9*(-1)^n)/4.

G.f.: x*(1 + x + 9*x^2)/((1+x)(1-x)^2).

a(n) = a(n-2) + 11. (End)

a(n) = 11*n - a(n-1) - 19 (with a(1)=1). - Vincenzo Librandi, Nov 25 2010

Mathematica

Rest@ CoefficientList[Series[x (1 + x + 9 x^2)/((1 + x) (1 - x)^2), {x, 0, 56}], x] (* or *)
Nest[Append[#1, #1[[-1]] + 1 + 9 Boole[EvenQ@ #2]] & @@ {#, Length@ #} &, {1}, 55] (* Michael De Vlieger, Nov 23 2018 *)
nxt[{n_, a_}]:={n+1, If[OddQ[n], a+1, a+10]}; NestList[nxt, {1, 1}, 60][[All, 2]] (* or *) LinearRecurrence[{1, 1, -1}, {1, 2, 12}, 60] (* Harvey P. Dale, Jun 22 2021 *)

Crossrefs

Sequence in context: A178362 A299961 A339139 * A032931 A072483 A081539

Adjacent sequences: A143792 A143793 A143794 * A143796 A143797 A143798

Keyword

nonn,easy

Author

Luis Farfan (ljfarfan(AT)gmail.com), Sep 01 2008

Extensions

Extended by R. J. Mathar, Sep 04 2008

New name from Michael De Vlieger, Nov 24 2018

Status

approved