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%I #9 Jun 13 2020 03:23:12
%S 6,9,12,14,18,20,33,44,62,70,92,108,116,138,164,175,212,254,280,308,
%T 320,332,348,356,452,490,524,558,572,692,716,764,833,932,956,1004,
%U 1105,1124,1172,1188,1436,1496,1562,1593,1676,1724,1772,1964,2002,2036,2088,2132
%N Numbers k such that psi(k) = psi(k + 2) where psi(k) is the Dedekind psi function (A001615).
%H Amiram Eldar, <a href="/A330703/b330703.txt">Table of n, a(n) for n = 1..10000</a>
%H Jozsef Sandor, <a href="https://www.emis.de/journals/JIPAM/article546.html">On the composition of some arithmetic functions, II</a>, Journal of Inequalities in Pure and Applied Mathematics, Vol. 6, No. 3 (2005), Article 73.
%e 6 is in the sequence since psi(6) = psi(8) = 12.
%t psi[1] = 1; psi[n_] := n * Times @@ (1 + 1/Transpose[FactorInteger[n]][[1]]); Select[Range[10^3], psi[#] == psi[# + 2] &]
%Y Cf. A001494, A001615, A007373, A062832, A291043.
%K nonn
%O 1,1
%A _Amiram Eldar_, Dec 26 2019
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