OFFSET
1,1
COMMENTS
a(5) consists of 93 and a(6) consists of 159 3's sandwiched between two 1's. - Sascha Kurz, Mar 26 2002
a(8) has 1471 digits. - Michael S. Branicky, Jan 27 2023
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..7
Patrick De Geest, PDP Reference Table - 131.
Makoto Kamada, Prime numbers of the form 133...331.
MATHEMATICA
Select[Flatten[Table[10*FromDigits[PadRight[{1}, n, 3]]+1, {n, 120}]], PrimeQ] (* Harvey P. Dale, Aug 09 2020 *)
PROG
(Python)
from sympy import isprime
from itertools import count, islice
def agen(): yield from (t for i in count(0) if isprime(t:=int("1" + "3"*i + "1")))
print(list(islice(agen(), 7))) # Michael S. Branicky, Jan 27 2023
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Feb 28 2002
EXTENSIONS
More terms from Sascha Kurz, Mar 26 2002
Edited by Ray Chandler, Nov 04 2014
STATUS
approved