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 A100897 #13 Jan 24 2020 09:54:15
%S A100897 7007,7117,7227,7337,7447,7557,7667,7777,7887,7997,710107,711117,
%T A100897 712127,713137,714147,715157,716167,717177,718187,719197,720207,
%U A100897 721217,722227,723237,724247,725257,726267,727277,728287,729297,730307
%N A100897 a(n) is the decimal expansion of 7nn7.
%H A100897 Daniel Starodubtsev, <a href="/A100897/b100897.txt">Table of n, a(n) for n = 0..10000</a>
%F A100897 a(n) = 7nn7.
%e A100897 If n=6, 7nn7 is 7667.
%e A100897 If n=15, 7nn7 is 715157 (a prime)
%e A100897 If n=18, 7nn7 is 718187 (a prime)
%e A100897 If n=19, 7nn7 is 719197 (a prime)
%p A100897 a:= n-> parse(cat(7,n,n,7)):
%p A100897 seq(a(n), n=0..35); # _Alois P. Heinz_, Jan 24 2020
%t A100897 Table[idn=IntegerDigits[n];FromDigits[Join[{7},idn,idn,{7}]],{n,0,30}] (* _Harvey P. Dale_, May 14 2013 *)
%Y A100897 Cf. A100846.
%K A100897 nonn,base,easy
%O A100897 0,1
%A A100897 _Parthasarathy Nambi_, Jan 10 2005