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 A093172 #33 Dec 13 2024 11:41:13
%S A093172 7,97,997,99999999999999997
%N A093172 Primes of the form 10^n - 3.
%C A093172 Primes of the form (9*10^n - 27)/9. - _Vincenzo Librandi_, Nov 16 2010
%C A093172 Also primes of the form 9*R_n - 2, where R_n is the repunit (A002275) of length n.
%C A093172 The next term has 140 digits.
%C A093172 a(n) = 10^A089675(n) - 3 = 10^(A056662(n) + 1) - 3. - _Farideh Firoozbakht_, Nov 27 2013
%H A093172 Makoto Kamada, <a href="https://stdkmd.net/nrr/9/99997.htm#prime">Prime numbers of the form 99...997</a>.
%H A093172 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%t A093172 Do[If[PrimeQ[10^n - 3], Print[10^n - 3]], {n, 100}] (* _Farideh Firoozbakht_, Nov 27 2013 *)
%t A093172 Select[Table[FromDigits[PadLeft[{7},n,9]],{n,25}],PrimeQ] (* _Harvey P. Dale_, Dec 12 2020 *)
%o A093172 (PARI) for(n=1,9, if(isprime(p=10^n-3), print1(p", "))) \\ _Charles R Greathouse IV_, Dec 13 2024
%Y A093172 Subsequence of A020471 and hence of A030096.
%Y A093172 Cf. A002275, A056662, A089675.
%K A093172 nonn
%O A093172 1,1
%A A093172 _Rick L. Shepherd_, Mar 26 2004
%E A093172 Name shortened and old name moved to comments by _Alex Ratushnyak_, Apr 26 2012