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 A048989 #20 Jan 15 2023 02:08:53 %S A048989 3,4,5,6,11,12,17,18,31,32,33,34,35,36,41,42,59,60,67,68,69,70,83,84, %T A048989 85,86,87,88,109,110,111,112,127,128,129,130,157,158,159,160,161,162, %U A048989 179,180,191,192,211,212,213,214,215,216,217,218,219 %N A048989 Numbers k such that pi(k) is prime. %C A048989 A000720(a(n)) is prime. - _Omar E. Pol_, Dec 19 2008 %H A048989 T. D. Noe, <a href="/A048989/b048989.txt">Table of n, a(n) for n = 1..10000</a> %t A048989 Select[Range[250],PrimeQ[PrimePi[#]]&] (* _Harvey P. Dale_, Mar 23 2011 *) %o A048989 (PARI) isok(k) = isprime(primepi(k)); \\ _Michel Marcus_, Jan 15 2023 %Y A048989 Cf. A000720. %K A048989 nonn,easy,nice %O A048989 1,1 %A A048989 _G. L. Honaker, Jr._