A162729 a(n) = 5^n*(5^n-1)/2.

0, 10, 300, 7750, 195000, 4881250, 122062500, 3051718750, 76293750000, 1907347656250, 47683710937500, 1192092871093750, 29802322265625000, 745058059082031250, 18626451489257812500, 465661287292480468750

Offset: 0

Author

Vincenzo Librandi, Jul 12 2009

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..500
• Index entries for linear recurrences with constant coefficients, signature (30, -125).

Programs

Magma

[5^n*(5^n-1)/2: n in [0..20]]; // Vincenzo Librandi, Mar 05 2012

Mathematica

n5[n_]:=Module[{c=5^n},(c(c-1))/2];Array[n5,20,0] (* or *) LinearRecurrence[ {30,-125},{0,10},20] (* Harvey P. Dale, Oct 25 2011 *)

Formula

a(n) = A000217(A000351(n)-1) = 30*a(n-1)-125*a(n-2). G.f.: 10*x/((25*x-1)*(5*x-1)). - R. J. Mathar, Jul 13 2009

Extensions

Edited by R. J. Mathar, Jul 13 2009