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 A154297 #14 Jan 06 2013 15:57:40
%S A154297 5,11,41,43
%N A154297 Primes of the form (1+2+3+...+m)/21 = A000217(m)/21, for some m.
%C A154297 This asks for primes p which are a triangular number divided by 21, or, 2*3*7*p=k*(k+1) for some k. Matching factors shows that the sequence is complete [_R. J. Mathar_, Aug 15 2010]
%C A154297 Original definition: Primes of the form : 1/x+2/x+3/x+4/x+5/x+6/x+7/x+..., x=21.
%C A154297 The corresponding m-values are m=14, 21, 41, 42 (cf. A154296). It is clear that for m>42, A000217(m)/21 = m(m+1)/42 cannot be a prime. - _M. F. Hasler_, Dec 31 2012
%t A154297 lst={};s=0;Do[s+=n/21;If[Floor[s]==s,If[PrimeQ[s],AppendTo[lst,s]]],{n,0,9!}];lst
%t A154297 #/21&/@Select[Accumulate[Range[100]],PrimeQ[#/21]&] (* _Harvey P. Dale_, Dec 17 2012 *)
%o A154297 (PARI) select(x->denominator(x)==1 & isprime(x), vector(42, m, m^2+m)/42) \\ - _M. F. Hasler_, Dec 31 2012
%Y A154297 Cf. A057570, A154293, A154296, A154298, A154299, A154300, A154301, A154302, A154303, A154304.
%K A154297 nonn,fini,full,easy
%O A154297 1,1
%A A154297 _Vladimir Joseph Stephan Orlovsky_, Jan 06 2009
%E A154297 Added keywords fini,full - _R. J. Mathar_, Aug 15 2010
%E A154297 Edited by _M. F. Hasler_, Dec 31 2012