This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
a(n) = for(k=2^(n-1), 2^n-1, v=binary(k); if(ispseudoprime(p=fromdigits(v)), return(p))); 0; \\ Jinyuan Wang, Mar 09 2020
Do[p = 2(10^n - 1)/9; k = 0; While[ ! PrimeQ[p], k++; p = FromDigits[ PadLeft[ IntegerDigits[k, 2], n] + 2]]; Print[p], {n, 1, 30}] (* Robert G. Wilson v, Apr 20 2002 *)
Table[SelectFirst[FromDigits/@Tuples[{2,3},n],PrimeQ],{n,20}] (* Harvey P. Dale, Nov 07 2021 *)
from sympy import isprime
from itertools import product
def a(n):
for b in product("01", repeat=n):
m = int("".join(b).replace("0", "2").replace("1", "3"))
if isprime(m): return m
return None
print([a(n) for n in range(1, 21)]) # Michael S. Branicky, Feb 23 2021 after Robert G. Wilson v
Flatten[Table[Select[FromDigits/@Tuples[{1, 4}, n], PrimeQ, 1], {n, 25}]/.{}->{0}] (* Jinyuan Wang, Mar 09 2020 *)
Flatten[Table[Select[FromDigits/@Tuples[{1, 7}, n], PrimeQ, 1], {n, 25}]/.{}->{0}] (* Jinyuan Wang, Mar 09 2020 *)
Table[SelectFirst[FromDigits/@Tuples[{3,4},n],PrimeQ],{n,18}] (* The program uses the SelectFirst function from Mathematica version 10 *) (* Harvey P. Dale, May 29 2015 *)
Flatten[Table[Select[FromDigits/@Tuples[{4,7},n],PrimeQ,1],{n,22}]/.{}->{0}] (* Harvey P. Dale, Jun 28 2012 *)
Table[SelectFirst[10#+9&/@FromDigits/@Tuples[{8,9},n-1],PrimeQ],{n,20}]/. (Missing["NotFound"]->0) (* Harvey P. Dale, Feb 01 2018 *)
Flatten[Table[Select[FromDigits/@Tuples[{1,3},n],PrimeQ,1],{n,18}]] (* Harvey P. Dale, Jul 23 2012 *)
Table[SelectFirst[FromDigits/@Tuples[{1,5},n],PrimeQ],{n,20}] (* Harvey P. Dale, Aug 04 2019 *)
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