OFFSET
1,1
LINKS
P. De Geest, SUPP Reference Table
EXAMPLE
12121212121 is prime so 5 appears in the sequence.
MATHEMATICA
Do[m = n; If[PrimeQ[120(10^(2n) - 1)/99 + 1], Print[n]], {n, 1, 600}]
(IntegerLength[#]-1)/2&/@Select[10#+1&/@Table[FromDigits[Flatten[ IntegerDigits/@ PadRight[{}, n, {1, 2}]]], {n, 2, 15000, 2}], PrimeQ] (* Harvey P. Dale, Apr 02 2020 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Robert G. Wilson v, Aug 22 2000
EXTENSIONS
More terms from Rick L. Shepherd, Mar 04 2004
STATUS
approved