A168458 a(n) = 7 + 10*floor((n-1)/2).

7, 7, 17, 17, 27, 27, 37, 37, 47, 47, 57, 57, 67, 67, 77, 77, 87, 87, 97, 97, 107, 107, 117, 117, 127, 127, 137, 137, 147, 147, 157, 157, 167, 167, 177, 177, 187, 187, 197, 197, 207, 207, 217, 217, 227, 227, 237, 237, 247, 247, 257, 257, 267, 267, 277, 277, 287

Offset: 1

Author

Vincenzo Librandi, Nov 26 2009

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000
• Index entries for linear recurrences with constant coefficients, signature (1,1,-1).

Crossrefs

Cf. A017353.

Programs

Magma

[7+10*Floor((n-1)/2): n in [1..70]]; // Vincenzo Librandi Sep 19 2013

Maple

A168458:=n->7 + 10*floor((n-1)/2); seq(A168458(k), k=1..100); # Wesley Ivan Hurt, Nov 08 2013

Mathematica

Table[7 + 10 Floor[(n - 1)/2], {n, 70}] (* or *) CoefficientList[Series[(7 + 3 x^2)/((1 + x) (x - 1)^2), {x, 0, 70}], x] (* Vincenzo Librandi, Sep 19 2013 *)
LinearRecurrence[{1,1,-1},{7,7,17},60] (* Harvey P. Dale, Apr 12 2018 *)

Formula

a(n) = 10*n - a(n-1) - 6, with n>1, a(1)=7.

G.f.: x*(7 + 3*x^2)/((1+x)*(x-1)^2). - Vincenzo Librandi, Sep 19 2013

a(n) = a(n-1) +a(n-2) -a(n-3). - Vincenzo Librandi, Sep 19 2013

From G. C. Greubel, Jul 23 2016: (Start)

a(n) = (10*n - 5*(-1)^n - 1)/2.

E.g.f.: (1/2)*(-5 + 6*exp(x) + (10*x - 1)*exp(2*x))*exp(-x). (End)

Extensions

New definition by Vincenzo Librandi, Sep 19 2013