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 A081677 #34 Sep 08 2022 08:45:09
%S A081677 0,1,3,5,6,7,12,16,17,22,24,35,115,120,358,1488,1819,4679,9821,27217,
%T A081677 27693,194413
%N A081677 Numbers n such that 2*10^n + 3 is prime.
%C A081677 a(22) > 10^5. - _Robert Price_, Nov 16 2014
%C A081677 a(23) > 2*10^5. - _Robert Price_, Jul 11 2015
%D A081677 Mark A. Herkommer, Number Theory, A Programmer's Guide, McGraw-Hill, New York, 1999, page 51.
%H A081677 Makoto Kamada, <a href="https://stdkmd.net/nrr/2/20003.htm#prime">Prime numbers of the form 200...003</a>.
%H A081677 Sabin Tabirca and Kieran Reynolds, <a href="http://multimedia.ucc.ie/Staff/ST/articles/SNJ03_Tabirca1.ps">Lacunary Prime Numbers</a>.
%F A081677 a(n) = A101951(n-1) + 1.
%e A081677 2+3 is prime, so are 23, 2003, 200003, 2000003, 20000003,2000000000003, etc. which are all of the form 2*10^n +3.
%t A081677 Do[ If[ PrimeQ[2*10^n + 3], Print[n]], {n, 0, 10000}]
%t A081677 Select[Range[0, 1000], PrimeQ[(2 10^# + 3)] &] (* _Vincenzo Librandi_, Nov 17 2014 *)
%o A081677 (Magma) [n: n in [0..500] | IsPrime(2*10^n+3)]; // _Vincenzo Librandi_, Nov 17 2014
%o A081677 (PARI) is(n)=isprime(2*10^n+3) \\ _Charles R Greathouse IV_, Feb 17 2017
%Y A081677 Cf. A101951.
%K A081677 more,nonn
%O A081677 1,3
%A A081677 _Robert G. Wilson v_, Mar 26 2003
%E A081677 More terms from _Robert G. Wilson v_, Jan 18 2005
%E A081677 a(20)-a(21) from Kamada data by _Robert Price_, Dec 09 2010
%E A081677 a(22) from _Robert Price_, Jul 11 2015