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 A228828 #20 Jul 04 2018 20:17:38 %S A228828 2,3,7,12,18,21,36,37,42,45,52,55,60,61,65,68,70,79,84,95,98,113,130, %T A228828 135,143,145,155,180,181,185,195,205,216,222,231,239,253,262,273,275, %U A228828 325,332,334,354,368,370,385,402,417,421,432,433,454,462,488,505,516 %N A228828 Numbers n such that n^2 + pi(n) is prime. %C A228828 Conjecture: the sequence is infinite. %H A228828 K. D. Bajpai and Charles R Greathouse IV, <a href="/A228828/b228828.txt">Table of n, a(n) for n = 1..10000</a> (first 3000 terms from Bajpai) %e A228828 a(6) = 21 : n^2+pi(n ) = 21^2 + pi(21) = 441+8 = 449 which is a prime. %p A228828 with(numtheory): KD:= proc() local a; a:= n^2+pi(n); if isprime(a) then RETURN(n): fi; end: seq(KD(), n=1..2000); %t A228828 Select[Range[600],PrimeQ[#^2+PrimePi[#]]&] (* _Harvey P. Dale_, Jul 04 2018 *) %o A228828 (PARI) v=List(); p=0; for(n=2,1e4,p+=isprime(n); if(isprime(n^2+p), listput(v, n))); Vec(v) \\ _Charles R Greathouse IV_, Sep 04 2013 %Y A228828 Cf. A064711, A064712. %Y A228828 Cf. A077510 (numbers n such that n + pi(n) is a prime). %K A228828 nonn %O A228828 1,1 %A A228828 _K. D. Bajpai_, Sep 04 2013