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%I #23 Jan 02 2023 12:30:54
%S 2,3,4,5,144,7,8,9,400,11,64281600,13,84672,129600,16,17,518400,19,
%T 4327213363200,254016,6326996189184000000,23,300174920860041216000,25,
%U 2747437056,27,3136,29
%N a(n) is the least integer m such that A047994(m) = ((n-1)/n)*m where A047994 is the unitary totient function, or 0 if there is no such m.
%C If it is not 0, a(30) > 10^30. - _Michel Marcus_, Sep 08 2018
%H Yasutoshi Kohmoto, <a href="http://list.seqfan.eu/oldermail/seqfan/2018-August/018717.html">UnitaryPhi</a>, SeqFan list, Aug 31 2018.
%H Michel Marcus, <a href="/A318842/a318842.gp.txt">solve_uphi pari code</a>
%F a(pp) = pp iff pp is a prime power (A000961) > 1.
%o (PARI) \\ uses the "solve_uphi pari code", see links
%o a(n) = {my(lim = 1, v); while (1, v = solve_uphi(n-1, n, lim); if (#v, return (v[1])); lim *= 10;);}
%Y Cf. A000961 (primepowers), A047994 (unitary totient).
%Y Cf. A030163, A305678.
%Y Cf. A145680 (analog with unitary sigma).
%K nonn,more
%O 2,1
%A _Michel Marcus_, Sep 04 2018
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