%I #34 Aug 09 2024 05:05:13

%S 76667,700666007,700000666000007,70000006660000007

%N Subsequence of beastly primes (A186086) that are palindromes that begin and end with 7.

%C Next term is 7_{0}^48_666_{0}^48_7, containing 101 digits, and is too large to include here.

%C The number of digits in the terms is 2*A186521(n)+3: 5, 9, 15, 17, 101, 1159, 1589, 2647, 2787, 4787, 6135, 26961 (some correspond to probable primes). - _Jens Kruse Andersen_, Jul 13 2014

%H Jens Kruse Andersen, <a href="/A046720/b046720.txt">Table of n, a(n) for n = 1..7</a>

%H R. Ondrejka, <a href="http://www.utm.edu/research/primes/lists/top_ten/">The Top Ten: a Catalogue of Primal Configurations</a>

%H Tony Padilla and Brady Haran, <a href="https://www.youtube.com/watch?v=zk_Q9y_LNzg">The Most Evil Number</a>, Numberphile video (2018)

%F a(n) = (7*10^(k+2)+666)*10^k+7, where k = A186521(n). - _Jens Kruse Andersen_, Jul 13 2014

%t Select[Table[(7*10^(n + 2) + 666)*10^n + 7, {n, 7}], PrimeQ] (* _Arkadiusz Wesolowski_, Sep 08 2011 *)

%t Select[Table[With[{s=PadRight[{7},n,0]},FromDigits[Join[s,{6,6,6},Reverse[s]]]],{n,8}],PrimeQ] (* _Harvey P. Dale_, Aug 05 2024 *)

%Y Cf. A051003, A131645, A186086, A186521.

%K base,nonn

%O 1,1

%A _G. L. Honaker, Jr._

%E Definition revised by _N. J. A. Sloane_, Feb 14 2011