|
|
A068645
|
|
Primes in which a string of 3's is sandwiched between two 1's.
|
|
9
|
|
|
|
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
|
|
LINKS
|
|
|
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")))
|
|
CROSSREFS
|
|
|
KEYWORD
|
base,nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|