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Numbers k such that sigma(k) + phi(k) is a perfect square.
2

%I #19 Jun 29 2018 02:16:48

%S 2,4,56,110,125,161,287,391,418,423,511,588,609,675,721,799,910,935,

%T 1048,1057,1102,1130,1281,1351,1457,1485,1630,1716,1799,1826,1921,

%U 2047,2060,2177,2255,2378,2403,2449,2457,2472,3199,3266,3915,4010,4376,4417

%N Numbers k such that sigma(k) + phi(k) is a perfect square.

%H Harry J. Smith, <a href="/A062784/b062784.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[4500],IntegerQ[Sqrt[DivisorSigma[1,#]+EulerPhi[#]]]&] (* _Harvey P. Dale_, Jan 18 2012 *)

%o (PARI) select(k->issquare(sigma(k) + eulerphi(k)), [1..5000])

%Y Cf. A065387.

%K nonn

%O 1,1

%A _Jason Earls_, Jul 18 2001