OFFSET
1,1
COMMENTS
No more terms through 10^4.
No more terms through 5*10^4. - Michael S. Branicky, Jun 30 2024
MATHEMATICA
s = 0; Do[s += (x-1)*5^(x-1)/5; If[PrimeQ[s], Print[x]], {x, 10^4}]
Select[Range[2100], PrimeQ[Sum[x*5^(x-1), {x, #-1}]]&] (* Harvey P. Dale, Feb 09 2023 *)
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Ryan Propper, Jan 01 2007
EXTENSIONS
Name simplified by Jon E. Schoenfield, Sep 23 2018
STATUS
approved