%I #29 Sep 29 2023 03:36:30

%S 1,81,121,361,1352569,2140369,6416089,9186961,30261001,108056025,

%T 820765201,2331248089,170938421809,8189950752481,8870860603201,

%U 33527956250889,136943052939289,149526943190641,4953581020385761,509672946670475329,578899033007097609,2043000477545048329

%N Perfect squares in A005728.

%e a(3) = 361 because A005728(34) = 361 and 361 is 19 squared.

%o (PARI) f(n)=1+sum(k=1, n, eulerphi(k)); \\ A005728

%o select(x->issquare(x), apply(f, [0..10^5])) \\ _Michel Marcus_, Sep 28 2023

%Y Cf. A000290, A005728.

%K nonn

%O 1,2

%A _Stuart E Anderson_, Sep 28 2023

%E a(11)-a(12) from _Michel Marcus_, Sep 28 2023

%E a(13)-a(22) from _Hugo Pfoertner_, Sep 28 2023