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 A166743 #12 May 16 2020 14:57:34
%S A166743 1,13,321,1337,21797,87321,1398013,89478345,357913781,22906492017,
%T A166743 366503875645,1466015503393,23456248058853,1501199875789697,
%U A166743 96076792050570001,384307168202281705,24595658764946068073
%N A166743 a(n) = (2^p - p^2 - 1)/6 where p = prime(n).
%H A166743 Harvey P. Dale, <a href="/A166743/b166743.txt">Table of n, a(n) for n = 3..468</a>
%F A166743 a(n) = (A034785(n) - A066872(n))/6. - _R. J. Mathar_, Oct 25 2009
%p A166743 A166743 := proc(n) p := ithprime(n) ; (2^p-p^2-1)/6 ; end: seq(A166743(n),n=3..20) ; # _R. J. Mathar_, Oct 25 2009
%t A166743 Table[(2^p-p^2-1)/6,{p,Prime[Range[3,20]]}] (* _Harvey P. Dale_, May 16 2020 *)
%Y A166743 Cf. A034785, A066872.
%K A166743 nonn
%O A166743 3,2
%A A166743 Tanin (Mirza Sabbir Hossain Beg) (mirzasabbirhossainbeg(AT)yahoo.com), Oct 21 2009
%E A166743 Missing exponentiation signs inserted in the definition by _R. J. Mathar_, Oct 25 2009
%E A166743 Corrected by _D. S. McNeil_, Aug 20 2010