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 A087269 #17 Oct 21 2019 11:03:49
%S A087269 1,9,12,18,21,25,26,28,32,34,35,36,42,45,49,52,55,57,60,65,68,69,70,
%T A087269 74,76,81,84,85,86,87,88,91,95,98,99,104,106,110,111,112,119,121,128,
%U A087269 129,130,133,135,141,143,145,147,155,158,159,160,161,162,165,170,172,177
%N A087269 Nonprime solutions to gcd(x, pi(x)) = gcd(x, A000720(x)) = 1.
%C A087269 What is the density of this sequence? - _David A. Corneth_, Oct 21 2019
%H A087269 David A. Corneth, <a href="/A087269/b087269.txt">Table of n, a(n) for n = 1..10000</a>
%e A087269 There are 37 primes below the nonprime 162, so pi(162) = 37 and as gcd(162, pi(162)) = gcd(162, 37) = 1, 162 is in the sequence. - _David A. Corneth_, Oct 21 2019
%t A087269 t=Table[GCD[w, PrimePi[w]], {w, 1, 1000}]; f=Flatten[Position[t, 1]]; cf=Part[f, Flatten[Position[PrimeQ[f], False]]]
%o A087269 (PARI) first(n) = {n = max(n, 2); my(q = 2, i = 1, t = 1, res = vector(n)); res[1] = 1; forprime(p = 3, oo, for(j = q + 1, p - 1, if(gcd(t, j) == 1, i++; if(i <= n, res[i] = j; , return(res); ) ) ); t++; q = p ) } \\ _David A. Corneth_, Oct 21 2019
%Y A087269 Cf. A000720, A007053, A057809, A087266, A087267, A087268.
%K A087269 nonn,easy
%O A087269 1,2
%A A087269 _Labos Elemer_, Sep 16 2003