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.
%I A320256 #43 Nov 14 2018 15:30:41
%S A320256 3,5,7,23,29,41,43,47,61,67,83,89,223,227,229,443,449,661,881,883,887,
%T A320256 2221,4441,4447,6661,8887,22229,44449,88883,444443,444449,666667,
%U A320256 888887,22222223,66666667,88888883,222222227,444444443,666666667,888888883,888888887
%N A320256 k-digit primes with the same even digit repeated k-1 times and a single odd digit.
%C A320256 For the resulting number to be prime, the rightmost digit must be the odd one. - _Michel Marcus_, Oct 11 2018
%H A320256 Alois P. Heinz, <a href="/A320256/b320256.txt">Table of n, a(n) for n = 1..132</a>
%e A320256 3, 5, 7 are in the sequence for k = 1.
%e A320256 229 is in the sequence because it is a 3-digit prime with the first 3-1 digits repeating even (2) and the last digit odd (9). - _David A. Corneth_, Oct 10 2018
%t A320256 Join[{3, 5, 7}, Select[Flatten@ Table[{1, 3, 7, 9} + 10 FromDigits@ ConstantArray[k, n], {n, 9}, {k, Range[2, 8, 2]}], PrimeQ]] (* _Michael De Vlieger_, Oct 31 2018 *)
%o A320256 (PARI) first(n) = {n = max(n, 3); my(t = 3, res = List([3, 5, 7])); print1("3, 5, 7, "); for(i=1, oo, k=(10^i - 1) / 9; forstep(f = 2, 8, 2, forstep(d=1, 9, 2, c = 10 * f * k + d; if(isprime(c), print1(c", "); listput(res, c); t++; if(t>=n, return(res))))))} \\ _David A. Corneth_, Oct 10 2018
%Y A320256 Cf. A055558, A068690, A105975, A141311, A154764.
%K A320256 nonn,base
%O A320256 1,1
%A A320256 _Enrique Navarrete_, Oct 08 2018
%E A320256 More terms from _Michel Marcus_, Oct 10 2018