A182775 Giza nonprimes.

1, 4, 6, 8, 9, 121, 232, 343, 454, 565, 676, 898, 12321, 23432, 45654, 56765, 67876, 78987, 1234321, 2345432, 3456543, 4567654, 5678765, 6789876, 123454321, 234565432, 456787654, 567898765, 12345654321, 23456765432, 45678987654

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.

Links

Table of n, a(n) for n=1..31.

Formula

A018252 INTERSECT A134810.

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

Cf. A018252, A134810, A134811, A134941, A182776.

Sequence in context: A202266 A232541 A076612 * A046354 A046357 A227947

Adjacent sequences: A182772 A182773 A182774 * A182776 A182777 A182778

Keyword

nonn,base,easy,fini

Author

Omar E. Pol, Dec 16 2010

Status

approved