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 A117048 #18 Sep 24 2018 16:53:14
%S A117048 2,7,11,13,29,31,37,43,61,67,73,79,83,97,101,127,137,139,151,157,163,
%T A117048 181,191,193,199,211,227,241,263,277,281,307,331,353,367,373,379,389,
%U A117048 409,421,433,443,461,463,487,499,541,571,577,587,601,619,631,659,661
%N A117048 Prime numbers that are expressible as the sum of two positive triangular numbers.
%C A117048 If the triangular number 0 is allowed, only one additional prime occurs: 3. In that case, the sequence becomes A117112.
%C A117048 A subsequence of A051533. - _Wolfdieter Lang_, Jan 11 2017
%H A117048 T. D. Noe, <a href="/A117048/b117048.txt">Table of n, a(n) for n = 1..10000</a>
%e A117048 2 = 1 + 1
%e A117048 7 = 1 + 6
%e A117048 11 = 1 + 10
%e A117048 13 = 10 + 3, etc.
%t A117048 tri = Table[n (n + 1)/2, {n, 40}]; Select[Union[Flatten[Outer[Plus, tri, tri]]], # <= tri[[-1]]+1 && PrimeQ[#] &] (* _T. D. Noe_, Apr 07 2011 *)
%o A117048 (PARI) is(n)=for(k=sqrtint(4*n+1)\2+1,(sqrtint(8*n+1)-1)\2, if(ispolygonal(n-k*(k+1)/2,3), return(n>3 && isprime(n)))); n==2 \\ _Charles R Greathouse IV_, Nov 07 2014
%Y A117048 Cf. A000040, A000217, A002243, A002244, A020756, A051533, A053614, A060773, A002636.
%K A117048 easy,nonn
%O A117048 1,1
%A A117048 _Andrew S. Plewe_, Apr 15 2006