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 A258140 #12 May 26 2015 10:59:26 %S A258140 0,0,1,1,1,2,2,1,1,3,3,3,0,2,2,3,2,1,2,2,3,3,2,2,2,3,3,2,0,4,4,5,1,4, %T A258140 4,2,2,2,3,3,3,5,1,3,3,4,4,1,2,3,4,3,1,5,4,5,1,1,3,4,6,4,2,3,2,6,7,3, %U A258140 2,2,3,5,3,4,4,4,5,2,5,2,4,6,1,5,2,5,5,2,3,3,4,4,2,4,5,6,3,2,4,5,6 %N A258140 Number of ways to write 6*n + 2 as p^2 + q with p and q both prime. %C A258140 Conjecture: a(n) > 0 except for n = 0, 1, 12, 28, 102, 117, 168, 4079. %C A258140 See also the comments in A258139. %H A258140 Zhi-Wei Sun, <a href="/A258140/b258140.txt">Table of n, a(n) for n = 0..10000</a> %e A258140 a(5) = 2 since 6*5 + 2 = 3^2 + 23 = 5^2 + 7 with 3, 23, 5, 7 all prime. %t A258140 Do[r=0;Do[If[PrimeQ[6n+2-Prime[k]^2],r=r+1],{k,1,PrimePi[Sqrt[6n+2]]}];Print[n," ",r];Continue,{n,0,100}] %o A258140 (PARI) a(n)=my(t=6*n+2,s); forprime(p=2,sqrtint(t-2), if(isprime(t-p^2), s++)); s \\ _Charles R Greathouse IV_, May 26 2015 %Y A258140 Cf. A000040, A002375, A258139, A258141. %K A258140 nonn %O A258140 0,6 %A A258140 _Zhi-Wei Sun_, May 22 2015