OFFSET
1,2
COMMENTS
The numbers formed by a(1) to a(8) are certified prime and those formed by a(9) and a(10) are prp's.
a(11) > 10000.
EXAMPLE
2 is a term since 277 is prime.
MATHEMATICA
Select[Range[1600], PrimeQ[#*10^# + 7*(10^# - 1)/9] &] (* Amiram Eldar, Jan 27 2021 *)
PROG
(PARI) isok(n) = { ss = Str(7*(10^n-1)/9); ispseudoprime(eval(concat(Str(n), ss))); } \\ Michel Marcus, Aug 09 2013
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Ray G. Opao, Sep 19 2007
EXTENSIONS
a(11) from Amiram Eldar, Jan 27 2021
a(12)-a(14) from Michael S. Branicky, Jun 06 2024
STATUS
approved