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 A073457 #22 Jun 23 2025 09:59:09
%S A073457 7,9,15,16,22,54,66,120,210
%N A073457 Numbers k such that phi(k) = pi(k) + 2.
%C A073457 Solutions to A000010(x) = A000720(x)+m, where m=+2; finite for any fixed value of m.
%e A073457 8 primes below 22 = {2,3,5,7,11,13,17,19}; 10 terms in RRS[22]={1,3,5,7,9,13,15,17,19,21}, so 22 is here.
%p A073457 with(numtheory): A073457:=n->`if`(phi(n) = pi(n) + 2, n, NULL): seq(A073457(n), n=1..210); # _Wesley Ivan Hurt_, May 12 2015
%t A073457 Do[s=EulerPhi[n]-PrimePi[n]; If[Equal[s, 2], Print[n]], {n, 10000}]
%t A073457 Select[Range[250],EulerPhi[#]-PrimePi[#]==2&] (* _Harvey P. Dale_, Jun 22 2025 *)
%o A073457 (Magma) [n: n in [2..1000] | EulerPhi(n) eq #PrimesUpTo(n)+2]; // _Vincenzo Librandi_, May 10 2015
%Y A073457 Cf. A037228, A037171, A000010, A000720, A073455, A072456.
%K A073457 fini,full,nonn
%O A073457 1,1
%A A073457 _Labos Elemer_, Aug 02 2002