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 A186086 #47 Feb 16 2025 08:33:14
%S A186086 6661,16661,66601,76667,700666007,6660000000001,666000000000001,
%T A186086 700000666000007,70000006660000007,6660000000000000000000000007,
%U A186086 66600000000000000000000000007,1000000000000066600000000000001
%N A186086 Beastly primes (version 1): either 666 followed by 0's and a 1 or 7 at the right end or a palindrome with 666 in the center, 0's surrounding these digits, and 1 or 7 at both ends.
%C A186086 Differs from A131645 in that 26669, 46663, 56663, 66617, 66629, 66643, 66653, 66683, 66697, 96661, 96667, 106661, 106663, 106669, 116663, 146669, 166601, 166603, 166609, 166613, 166619, 166627, 166631, 166643, 166657, 166667, 166669, 166679, are not included here.
%C A186086 76667 is the largest beastly prime that does not contain the digit "0".
%H A186086 Charles R Greathouse IV, <a href="/A186086/b186086.txt">Table of n, a(n) for n = 1..33</a>
%H A186086 Chris Caldwell, The Prime Glossary, <a href="https://t5k.org/glossary/xpage/BeastlyPrime.html">Beastly prime</a>
%H A186086 G. L. Honaker, Jr. and Chris Caldwell, <a href="https://t5k.org/curios/cpage/2774.html">Prime Curios! 6661</a>
%H A186086 R. Ondrejka, <a href="http://www.utm.edu/research/primes/lists/top_ten/">The Top Ten: a Catalogue of Primal Configurations</a> (May 2001), p. 5
%H A186086 Tony Padilla and Brady Haran, <a href="https://www.youtube.com/watch?v=zk_Q9y_LNzg">The Most Evil Number</a>, Numberphile video (2018)
%H A186086 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/BeastNumber.html">Beast Number</a>
%t A186086 e = 14; p = 666*10^n + 1; q = (10^(n + 2) + 666)*10^n + 1; Select[Union[Table[p, {n, 2*e}], Table[p + 6, {n, 2*e}], Table[q, {n, e}], Table[q + 6*10^(2*n + 2) + 6, {n, e}]], PrimeQ] (* _Arkadiusz Wesolowski_, Sep 21 2011 *)
%t A186086 Module[{nn=35,bp1,bp2,bp3,bp4}, bp1=FromDigits/@ Table[Join[PadRight[ {6,6,6},n1,0],{1}],{n1,3,nn}]; bp2=FromDigits/@ Table[Join[ PadRight[ {6,6,6},n2,0],{7}], {n2,3,nn}]; bp3=FromDigits/@ Table[Join[PadRight[ {1},n3,0], {6,6,6},PadLeft[ {1},n3,0]],{n3,1,nn/2}];bp4=FromDigits/@ Table[Join[PadRight[{7},n3,0],{6,6,6}, PadLeft[ {7},n3,0]],{n3,1,nn/2}]; Select[Sort[Join[bp1,bp2,bp3,bp4]],PrimeQ]] (* _Harvey P. Dale_, Jan 18 2017 *)
%Y A186086 Cf. A046720, A051003, A131645, A164968, A196023, A138563, A186630, A186538, A156166, A186521.
%K A186086 nonn,base,dumb
%O A186086 1,1
%A A186086 _Arkadiusz Wesolowski_, Feb 12 2011
%E A186086 Edited by _N. J. A. Sloane_, Feb 12 2011
%E A186086 a(10)-a(12) from _Charles R Greathouse IV_, Feb 12 2011