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%I #14 Apr 30 2022 08:21:20
%S 9,27,50,169,242,245,945,1127,1280,1352,1694,2430,4335,4410,4624,4802,
%T 7500,7935,8624,11913,12544,13254,15050,16384,24642,27869,29403,31827,
%U 33489,36750,39675,47045,52800,53290,55470,58806,66248,72075,74060,81675,90774,90972
%N Composite numbers k+1 such that k*phi(k+1) is a perfect square.
%C Trivially if k+1 is prime k*phi(k+1) = k^2. If k>1 k*phi(k) is never a perfect square.
%H Amiram Eldar, <a href="/A069068/b069068.txt">Table of n, a(n) for n = 1..1000</a>
%t Select[Range[60000], !PrimeQ[ #+1] && IntegerQ[Sqrt[ # EulerPhi[1+# ]]]&] (* _T. D. Noe_, Nov 01 2006 *)
%Y Cf. A000010, A000290.
%K easy,nonn
%O 1,1
%A _Benoit Cloitre_, Apr 05 2002
%E Corrected by _T. D. Noe_, Nov 01 2006
%E More terms from _Amiram Eldar_, Apr 29 2022