0,2

a(n)=4*(7^n-1)/6.

a(n)=7*a(n-1)+4 (with a(1)=0) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Oct 30 2009]

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

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

4.........................4

44.......................32

444.....................228

4444...................1600

44444.................11204

444444................78432

4444444..............549028

44444444............3843200

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

For n=2, a(2)=7*0+4=4; n=3, a(3)=7*4+4=32; n=4, a(4)=7*32+4=228 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Oct 30 2009]

seq(4*(7^n-1)/6, n=0..21);

Sequence in context: A098981 A120917 A099269 this_sequence A033515 A147551 A007278

Adjacent sequences: A125820 A125821 A125822 this_sequence A125824 A125825 A125826

easy,nonn

Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Feb 03 2007