A067811 - OEIS

%I #9 Aug 13 2019 11:23:11

%S 7,32,33,41,68,145,209,237,239,266,328,372,384,385,442,522,622,905,

%T 945,1157,1243,1288,1357,1581,1615,1643,1798,1853,1885,1978,1995,2093,

%U 2418,2541,2698,2765,2769,2981,3013,3161,3315,3451,3519,3577,4041,4309,4318

%N Numbers n such that phi(n)^2 + sigma(n)^2 is an integer square.

%H Amiram Eldar, <a href="/A067811/b067811.txt">Table of n, a(n) for n = 1..10000</a>

%e phi(32)^2 + sigma(32)^2 = 16^2 + 63^2 = 4225 = 65^2, so 32 is a term of the sequence.

%t Select[Range[10^4], IntegerQ[Sqrt[EulerPhi[ # ]^2 + DivisorSigma[1, # ]^2]] &]

%o (PARI) isok(n) = issquare(eulerphi(n)^2+sigma(n)^2); \\ _Michel Marcus_, Aug 13 2019

%Y Cf. A000010, A000203.

%K easy,nonn

%O 1,1

%A _Joseph L. Pe_, Feb 07 2002