OFFSET
1,1
COMMENTS
a(14) > 2*10^5. - Robert Price, Jan 25 2015
EXAMPLE
For k = 3, 6, 10 the corresponding primes are 7, 547, 83653.
MATHEMATICA
s = 0; Do[s += (x-1)*3^(x-2); If[PrimeQ[s], Print[x]], {x, 10^4}]
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Ryan Propper, Jan 01 2007
EXTENSIONS
a(10) from Max Alekseyev, Dec 10 2011
a(11)-a(13) from Robert Price, Jan 25 2015
STATUS
approved