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 A101398 #27 Jan 04 2025 16:02:32
%S A101398 1,2,14,20,30,44,66,260,872,8846,26744,57506,98472,106892
%N A101398 Numbers k such that 4*10^k-3 is prime.
%C A101398 See Kamada link for search limit and prime vs. PRP status.
%C A101398 a(14) > 10^5. - _Robert Price_, Mar 17 2015
%C A101398 a(15) > 2*10^5. - _Robert Price_, Oct 02 2015
%H A101398 Makoto Kamada, <a href="https://stdkmd.net/nrr/3/39997.htm#prime">Prime numbers of the form 399...997</a>.
%H A101398 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A101398 a(n) = A101849(n) + 1.
%e A101398 k = 1, 2, 14, 20 are members since 37, 397, 399999999999997 and 399999999999999999997
%e A101398 are prime numbers.
%t A101398 Do[ If[ PrimeQ[4*10^n - 3], Print[n]], {n, 0, 10000}]
%o A101398 (PARI) for(n=1, 1e4, if(isprime(4*10^n-3), print1(n", "))) \\ _Altug Alkan_, Oct 02 2015
%Y A101398 Cf. A089675, A101849.
%K A101398 nonn,more
%O A101398 1,2
%A A101398 Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005
%E A101398 a(11)-a(12) from Kamada data by _Robert Price_, Dec 13 2010
%E A101398 a(13) from Kamada data by _Robert Price_, Mar 17 2015
%E A101398 a(14) from _Robert Price_, Oct 02 2015