A168420 a(n) = 4 + 10*floor(n/2).

4, 14, 14, 24, 24, 34, 34, 44, 44, 54, 54, 64, 64, 74, 74, 84, 84, 94, 94, 104, 104, 114, 114, 124, 124, 134, 134, 144, 144, 154, 154, 164, 164, 174, 174, 184, 184, 194, 194, 204, 204, 214, 214, 224, 224, 234, 234, 244, 244, 254, 254, 264, 264, 274, 274, 284

Offset: 1

Author

Vincenzo Librandi, Nov 25 2009

Keywords

• nonn
• easy
• less

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. A017317, A168278.

Programs

Magma

[4+10*Floor(n/2): n in [1..70]]; // Vincenzo Librandi, Sep 19 2013

Mathematica

Table[4 + 10 Floor[n/2], {n, 70}] (* or *) CoefficientList[Series[(4 + 10 x - 4 x^2)/((1 + x) (x - 1)^2), {x, 0, 70}], x] (* Vincenzo Librandi, Sep 19 2013 *)

Formula

a(n) = 10*n - a(n-1) - 2, with n>1, a(1)=4.

G.f.: 2*x*(2 + 5*x - 2*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

a(n) = 2*A168278(n). - Bruno Berselli, Sep 19 2013

E.g.f.: (1/2)*(5 - 8*exp(x) + (10*x + 3)*exp(2*x))*exp(-x). - G. C. Greubel, Jul 22 2016

Extensions

New definition by Vincenzo Librandi, Sep 19 2013