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%I #5 Sep 20 2018 08:17:15
%S 1,2,6,12,168,240,14880,65280,4294901760,7608944640,1125874137169920,
%T 18446744069414584320
%N Integers k such that uphi(k) divides k, where uphi is the unitary phi function (A047994).
%H Tomohiro Yamada, <a href="https://arxiv.org/abs/1806.00647">An analog of perfect numbers involving the unitary totient function</a>, arXiv:1806.00647 [math.NT], 2018. See (2) on p. 2.
%o (PARI) uphi(n) = my(f=factor(n)~); prod(i=1, #f, f[1, i]^f[2, i]-1);
%o isok(n) = frac(n/uphi(n)) == 0;
%Y Cf. A047994.
%Y A030163 is a subsequence.
%K nonn,more
%O 1,2
%A _Michel Marcus_, Sep 20 2018
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