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 A063530 #25 Jul 08 2024 08:52:56
%S A063530 15,16,20,24,30,35,39,45,52,56,65,70,72,78,84,90,104,105,112,123,130,
%T A063530 140,143,144,155,156,164,165,168,175,176,180,183,200,203,210,215,220,
%U A063530 225,231,244,245,246,248,261,264,286,300,308,310,323,330,339,344,350
%N A063530 Numbers k such that phi(k)+1 is a square.
%C A063530 Numbers k such that A000010(k) = -1 + m^2 for some m.
%H A063530 Amiram Eldar, <a href="/A063530/b063530.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Harry J. Smith)
%e A063530 If k = p*(p+2), a product of twin primes (from A037074), then k is in the sequence. The corresponding square is p^2. Other solutions are k = {56,72,78,84}, since phi(k) + 1 = 25 for all. Also phi(123) + 1 = 9^2, the square of a composite.
%t A063530 Select[Range[400],IntegerQ[Sqrt[1+EulerPhi[#]]]&] (* _Harvey P. Dale_, Jul 31 2020 *)
%o A063530 (PARI) { n=0; for (a=1, 10^9, if (issquare(eulerphi(a) + 1), write("b063530.txt", n++, " ", a); if (n==1000, break)) ) } \\ _Harry J. Smith_, Aug 25 2009
%Y A063530 Cf. A000010, A037074, A039649.
%K A063530 nonn
%O A063530 1,1
%A A063530 _Labos Elemer_, Aug 02 2001