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 A056805 #40 Apr 15 2024 05:35:20
%S A056805 0,1,2,8,9,15,20,26,38,45,65,112,244,303,393,560,839,1009,1019,1173,
%T A056805 1334,2236,2629,4426,8848,20812,37744,72926,86287,231617,281969,
%U A056805 488852,522127,655642,758068,879313,1380098
%N A056805 Numbers k such that 6*10^k+1 is prime.
%C A056805 From the Kamada data, Edward Trice reports that 231617 and 522127 are in this sequence. But these may not be the next ones. There are no others less than 2*10^5, however. - _Robert Price_, Jul 09 2015
%H A056805 Makoto Kamada, <a href="https://stdkmd.net/nrr/6/60001.htm#prime">Prime numbers of the form 600...001</a>.
%H A056805 Sabin Tabirca and Kieran Reynolds, <a href="http://multimedia.ucc.ie/Staff/ST/articles/SNJ03_Tabirca1.ps">Lacunary Prime Numbers</a>.
%F A056805 a(n) = A101517(n-1) + 1.
%e A056805 For k=2 => (6*10^2+1)=601, which is prime.
%t A056805 Do[ If[ PrimeQ[ 6*10^n + 1], Print[ n ]], {n, 0, 10000}]
%o A056805 (PARI) is(n)=isprime(6*10^n+1) \\ _Charles R Greathouse IV_, Feb 17 2017
%Y A056805 Cf. A056716, A101517.
%K A056805 more,nonn
%O A056805 1,3
%A A056805 _Robert G. Wilson v_, Aug 22 2000
%E A056805 a(22)-a(25) from _Hugo Pfoertner_, Feb 11 2004
%E A056805 a(26)=20812 from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 27 2007
%E A056805 a(27)=37744 from _Jason Earls_, Mar 07 2008
%E A056805 a(28)-a(29) from Kamada data by _Robert Price_, Dec 09 2010
%E A056805 a(30)-a(36) from Kamada data by _Tyler Busby_, Apr 15 2024