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%I #21 Apr 06 2023 08:30:39
%S 1,3,15,84,217,255,1710,2967,5363,11242,24066,27370,29697,29953,60977,
%T 65535,69324,103257,159761,209305,228333,446516,598559,615410,691410,
%U 1231305,1238358,1365175,1467732,1841154,1966220,2081070,2562370
%N Numbers k such that phi(k)*k is a triangular number.
%H Amiram Eldar, <a href="/A115910/b115910.txt">Table of n, a(n) for n = 1..100</a>
%e phi(24066)*24066 = 164611440 = T(18144).
%t Select[Range[2.6*10^6],OddQ[Sqrt[8#*EulerPhi[#]+1]]&] (* _Harvey P. Dale_, Jul 11 2017 *)
%o (PARI) isok(n) = ispolygonal(n*eulerphi(n), 3); \\ _Michel Marcus_, Jan 25 2014
%Y Cf. A002618, A000217, A115905, A115909.
%K nonn
%O 1,2
%A _Giovanni Resta_, Feb 06 2006
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