A108903 Numbers such that the outer 2 digits are 9 and the inner digits are 5.

959, 9559, 95559, 955559, 9555559, 95555559, 955555559, 9555555559, 95555555559, 955555555559, 9555555555559, 95555555555559, 955555555555559, 9555555555555559, 95555555555555559, 955555555555555559

Offset

1,1

Comments

These numbers are all composite. They are divisible among other numbers by 3,7,11,13 depending on the form 6k+r, 0 < r < 6. See the link for a proof.

Links

Table of n, a(n) for n=1..16.

Cino Hilliard, Proof 955..559 is composite.

Index entries for linear recurrences with constant coefficients, signature (11, -10).

Formula

S(x)=9*10^(x+1)+ 9 + 50*(10^x-1)/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^x-1)/9; print(x", ") ) }

Crossrefs

Sequence in context: A226851 A351674 A158410 * A167780 A316338 A257417

Adjacent sequences: A108900 A108901 A108902 * A108904 A108905 A108906

Keyword

easy,nonn,base

Author

Cino Hilliard, Jul 16 2005

Status

approved