

A108904


Numbers such that the outer two digits are 9's and the inner digits are 7's.


0



979, 9779, 97779, 977779, 9777779, 97777779, 977777779, 9777777779, 97777777779, 977777777779, 9777777777779, 97777777777779, 977777777777779, 9777777777777779, 97777777777777779, 977777777777777779
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OFFSET

1,1


COMMENTS

These numbers are all composite. They are divisible by 3,7,11 or 13. See the link for a proof.


LINKS

Table of n, a(n) for n=1..16.
Cino Hilliard, Proof 977..779 is composite.


FORMULA

S(x)=9*10^(x+1) + 9 + 70*(10^x1)/9.


PROG

(PARI) g(n, r, m) = \Repeat rrr.. surrounded by 2 m's { for(x=1, n, y=m*10^(x+1)+m+r*10*(10^x1)/9; print1(y", ") )


CROSSREFS

Sequence in context: A231708 A172158 A327825 * A091080 A157515 A188337
Adjacent sequences: A108901 A108902 A108903 * A108905 A108906 A108907


KEYWORD

easy,nonn,base


AUTHOR

Cino Hilliard, Jul 16 2005


EXTENSIONS

Minor edits by N. J. A. Sloane, Aug 01 2010


STATUS

approved



