login
A108904
a(n) has two outer digits 9 and n inner digits 7.
1
99, 979, 9779, 97779, 977779, 9777779, 97777779, 977777779, 9777777779, 97777777779, 977777777779, 9777777777779, 97777777777779, 977777777777779, 9777777777777779, 97777777777777779, 977777777777777779, 9777777777777777779, 97777777777777777779, 977777777777777777779
OFFSET
0,1
COMMENTS
These numbers are all composite. They are divisible by 3,7 or 11.
All terms are divisible by 11. - Jason Yuen, Sep 02 2024
FORMULA
a(n) = 9*10^(n+1) + 9 + 70*(10^n-1)/9.
a(n) = 11*(80*10^n + 1)/9. - Jason Yuen, Sep 02 2024
From Alois P. Heinz, Sep 02 2024: (Start)
a(n) = 11*A059482(n+1).
G.f.: 11*(9-10*x)/((10*x-1)*(x-1)). (End)
PROG
(PARI) g(n, r=7, m=9) = /* Repeat rrr.. surrounded by 2 m's */ { for(x=0, n, y=m*10^(x+1)+m+r*10*(10^x-1)/9; print1(y", ") ) }
CROSSREFS
Cf. A059482.
Sequence in context: A061366 A177686 A135219 * A182672 A124113 A223157
KEYWORD
easy,nonn,base
AUTHOR
Cino Hilliard, Jul 16 2005
EXTENSIONS
Minor edits by N. J. A. Sloane, Aug 01 2010
a(0) prepended by Alois P. Heinz, Sep 02 2024
STATUS
approved