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(2)=883 is a term because all digits are equal to 8 except one.
a(2)=6661 is a term because all digits are equal to 6 except one.
Select[FromDigits/@Flatten[Table[PadLeft[{pd},n,6],{pd,{1,7}},{n,3,30}],1],PrimeQ]//Sort (* Harvey P. Dale, Sep 01 2021 *)
a(2)=449 is a term because all digits are equal to 4 except one.
Select[Flatten[Table[FromDigits[PadLeft[{n},x,4]],{x,3,30},{n,{1,3,7,9}}]],PrimeQ] (* Harvey P. Dale, Feb 18 2018 *)
5557 is a term because all digits are equal to 5 except one.
1117 is a term because all digits are equal to 1 except the last one.
3331 is a term because all digits are equal to 3 except the last one.
77773 is a term because all digits are equal to 7 except the last one.
99991 is a term because all digits are equal to 9 except the last one.
R:= NULL: count:= 0:
for n from 3 to 999 do
for d in [9,3] do
if isprime(10^n - d) then
R:= R, 10^n-d; count:= count+1;
fi
od od:
R;
Join[{11},Select[Flatten[Table[FromDigits[Join[PadRight[{},n,1],{d},PadRight[{},n,1]]],{n,26},{d,Cases[Range[0,9],Except[1]]}]],PrimeQ]] (* Harvey P. Dale, Nov 04 2024 *)
print1(11); for(L=1,19,for(d=0,9,d!=1 && ispseudoprime(p=10^(2*L+1)\9+(d-1)*10^L) && print1(","p))) \\ M. F. Hasler, Feb 07 2020
lst = {}; Do[If[PrimeQ[n] && SortBy[Tally[IntegerDigits[n]], Last][[-1, -1]] == IntegerLength[n] - 1, AppendTo[lst, n]], {n, 101, 10^3}]; lst (* Arkadiusz Wesolowski, Sep 18 2011 *)
lst = {}; Do[r = (10^n - 1)/9; Do[AppendTo[lst, DeleteCases[Select[FromDigits[Permutations[Append[IntegerDigits[a*r], d]]], PrimeQ], r | 2 | 3 | 5 | 7]], {a, 9}, {d, 0, 9}], {n, 2, 6}]; Sort[Flatten[lst]] (* Arkadiusz Wesolowski, Sep 22 2011 *)
from sympy import isprime
from itertools import count, islice
def agen(): # generator of terms
for d in count(3):
ds = set()
for end in "1379":
ds.update(int(c*(d-1) + end) for c in "123456789" if c != end)
for diff in "0123456789":
if end == diff: continue
cands = (end*i + diff + end*(d-1-i) for i in range(d-1))
ds.update(int(t) for t in cands if t[0] != "0")
yield from sorted(t for t in ds if isprime(t))
print(list(islice(agen(), 52))) # Michael S. Branicky, May 17 2022
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