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%I #8 Oct 05 2019 04:25:08
%S 300,2100,3300,3900,5100,5700,6900,8700,9300,11100,12100,12300,12900,
%T 14100,15900,17700,18300,20100,21300,21900,23100,23700,23760,24900,
%U 26700,27300,29100,30300,30900,32100,32700,33900,35700,38100,39300,39900,41100,41700,42900
%N Exponential (2,3)-perfect numbers: numbers m such that esigma(esigma(m)) = 3m, where esigma(m) is the sum of exponential divisors of m (A051377).
%C The exponential version of A019281.
%D J. Hanumanthachari, V. V. Subrahmanya Sastri, and V. Srinivasan, On e-perfect numbers, Math. Student, Vol. 46, No. 1 (1978), pp. 71-80.
%D József Sándor and Borislav Crstici, Handbook of Number theory II, Kluwer Academic Publishers, 2004, Chapter 1, p. 53.
%H Amiram Eldar, <a href="/A328132/b328132.txt">Table of n, a(n) for n = 1..10000</a>
%F 300 is in the sequence since esigma(300) = 540, and esigma(540) = 900 = 3*300.
%t f[p_, e_] := DivisorSum[e, p^# &]; esigma[1] = 1; esigma[n_] := Times @@ f @@@ FactorInteger[n]; espQ[n_] := esigma[esigma[n]] == 3n; Select[Range[50000], espQ]
%Y Cf. A019281, A051377, A064012.
%K nonn
%O 1,1
%A _Amiram Eldar_, Oct 04 2019