A168456 a(n) = (10*n - 5*(-1)^n + 1)/2.

8, 8, 18, 18, 28, 28, 38, 38, 48, 48, 58, 58, 68, 68, 78, 78, 88, 88, 98, 98, 108, 108, 118, 118, 128, 128, 138, 138, 148, 148, 158, 158, 168, 168, 178, 178, 188, 188, 198, 198, 208, 208, 218, 218, 228, 228, 238, 238, 248, 248, 258, 258, 268, 268, 278, 278, 288

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. A168280, A017365.

Programs

Magma

[8+10*Floor((n-1)/2): n in [1..70]]; // Vincenzo Librandi, Sep 19 2013

Mathematica

RecurrenceTable[{a[1]==8,a[n]==10n-a[n-1]-4},a,{n,60}] (* or *) LinearRecurrence[ {1,1,-1},{8,8,18},60] (* or *) With[{c=NestList[ 10+#&,8,30]},Riffle[c,c]] (* Harvey P. Dale, Aug 02 2013 *)
Table[8 + 10 Floor[(n - 1)/2], {n, 70}] (* or *)   CoefficientList[Series[2 (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) - 4, with n>1, a(1)=8.

a(1)=8, a(2)=8, a(3)=18; for n>3, a(n) = a(n-1) + a(n-2) - a(n-3). - Harvey P. Dale, Aug 02 2013

From R. J. Mathar, Aug 06 2013: (Start)

G.f. 2*x*(4 + x^2) / ( (1+x)*(x-1)^2 ).

a(n) = 2*A168280(n). (End)

a(n) = 8 + 10*floor((n-1)/2). - Vincenzo Librandi, Sep 19 2013

E.g.f.: (1/2)*(-5 + 4*exp(x) + (10*x + 1)*exp(2*x))*exp(-x). - G. C. Greubel, Jul 22 2016