0,2

a(n)=5*(7^n-1)/6.

a(n)=7*a(n-1)+5 (with a(1)=0) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Oct 30 2009]

Base 7.............decimal

0........................0

5........................5

55......................40

555....................285

5555..................2000

55555................14005

555555...............98040

5555555.............686285

55555555...........4804000

555555555.........33628005

etc....................etc...

For n=2, a(2)=7*0+5=5; n=3, a(3)=7*5+5=40; n=4, a(4)=7*40+5=285 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Oct 30 2009]

seq(5*(7^n-1)/6, n=0..21);

Sequence in context: A087632 A124306 A124545 this_sequence A144069 A073505 A145841

Adjacent sequences: A125726 A125727 A125728 this_sequence A125730 A125731 A125732

easy,nonn,new

Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Feb 02 2007