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%I #19 Jan 14 2017 07:56:49
%S 4,8,9,14,22,21,16,32,27,26,46,33,38,58,62,44,39,57,45,55,49,52,94,86,
%T 64,106,75,63,118,77,74,104,134,92,142,91,82,93,158,162,166,128,116,
%U 115,95,99,111,119,122,125,206,112,214,133,117,145,178,135,153,242
%N Smallest k > 2n+1 such that phi(k) = phi(2n+1).
%C All terms are composite.
%H Robert Israel, <a href="/A280450/b280450.txt">Table of n, a(n) for n = 1..10000</a>
%F 2n+1 < a(n) < 4n+3.
%F From _Robert Israel_, Jan 03 2017: (Start)
%F a(n)=2n+2 if and only if 2n+1 is in A001274.
%F If n > 3 is in A005384, then a(n)=4n+2. (End)
%p f:= n -> min(select(`>`,numtheory:-invphi(numtheory:-phi(2*n+1)),2*n+1)):
%p map(f, [$1..100]); # _Robert Israel_, Jan 03 2017
%t Table[k = 2 n + 2; While[EulerPhi@ k != #, k++] &@ EulerPhi[2 n + 1]; k, {n, 120}] (* _Michael De Vlieger_, Jan 03 2017 *)
%o (PARI) a(n) = my(k=2*n+2); while(eulerphi(k)!=eulerphi(2*n+1), k++); k \\ _Felix Fröhlich_, Jan 05 2017
%Y Cf. A000010, A001274, A005384, A140141.
%K nonn
%O 1,1
%A _Thomas Ordowski_, Jan 03 2017
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