OFFSET
1,1
COMMENTS
a(13) has 1003 digits. - Michael S. Branicky, Jan 27 2023
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..12
MATHEMATICA
Union[Flatten[Table[Select[Table[FromDigits[Join[{i}, PadRight[{}, n, 7], {i}]], {n, 100}], PrimeQ], {i, 1, 9, 2}]]] (* Harvey P. Dale, Nov 22 2012 *)
PROG
(PARI) n10np1(n, d) = { local(x, y, k); for(x=1, n, for(k=1, 8, y=10^(x+1)*k+floor(10^x*d/9)*10+k; if(isprime(y), print1(y", ")) ) ) }
(Python)
from sympy import isprime
from itertools import count, islice
def agen(): yield from (t for i in count(1) for f in "1379" if isprime(t:=int(f + "7"*i + f)))
print(list(islice(agen(), 12))) # Michael S. Branicky, Jan 27 2023
CROSSREFS
KEYWORD
easy,nonn,base
AUTHOR
Cino Hilliard, Jul 11 2005
EXTENSIONS
Name changed by Arkadiusz Wesolowski, Sep 07 2011
One more term (a(6)) added by Harvey P. Dale, Nov 22 2012
STATUS
approved