OFFSET
1,2
COMMENTS
I propose the name Giza nonprimes.
The total number of terms is 37. The largest is 12345678987654321 which is also the largest mountain number A134941.
EXAMPLE
a(6)=121 is in the sequence because 121 is a nonprime number A018252 and 121 is also a Giza number A134810.
The last six terms of this finite sequence are
a(32) = 1234567654321
a(33) = 2345678765432
a(34) = 3456789876543
a(35) = 123456787654321
a(36) = 234567898765432
a(37) = 12345678987654321
Illustration of a(37) as a Giza nonprime:
. . . . . . . . 9 . . . . . . . .
. . . . . . . 8 . 8 . . . . . . .
. . . . . . 7 . . . 7 . . . . . .
. . . . . 6 . . . . . 6 . . . . .
. . . . 5 . . . . . . . 5 . . . .
. . . 4 . . . . . . . . . 4 . . .
. . 3 . . . . . . . . . . . 3 . .
. 2 . . . . . . . . . . . . . 2 .
1 . . . . . . . . . . . . . . . 1
MATHEMATICA
Select[Union[FromDigits/@Select[Flatten[Table[Table[Join[Range[i, i+n], Reverse[ Most[ Range[ i, i+n]]]], {n, 0, 9}], {i, 9}], 1], Max[#]<10&]], !PrimeQ[#]&] (* Harvey P. Dale, Aug 23 2011 *)
CROSSREFS
KEYWORD
nonn,base,easy,fini
AUTHOR
Omar E. Pol, Dec 16 2010
STATUS
approved