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Positions of first appearances of odd primes in A137576.
6

%I #8 Jan 11 2019 09:58:12

%S 1,2,3,5,4,7,9,11,14,10,18,12,21,23,26,29,17,33,35,28,39,41,42,48,50,

%T 51,53,45,43,63,46,68,69,74,38,78,66,83,86,89,90,95,59,98,85,49,111,

%U 113,97,88,119,71,125,128,131,134,135,138,93,141,146,109,155,84,158,165,145

%N Positions of first appearances of odd primes in A137576.

%C a(n) <= (p_n-1)/2, where p_n is the n-th odd prime (A065091).

%t terms = 100;

%t a137576[n_] := Module[{t}, (t = MultiplicativeOrder[2, 2 n + 1])* DivisorSum[2 n + 1, EulerPhi[#]/MultiplicativeOrder[2, #] &] - t + 1];

%t A137576 = Array[a137576, 3 terms];

%t FirstPosition[A137576, #][[1]]& /@ Prime[Range[2, terms+1]] (* _Jean-François Alcover_, Jan 11 2019 *)

%Y Cf. A137576, A065091.

%K nonn

%O 1,2

%A _Vladimir Shevelev_, May 10 2008

%E Corrected and extended by _Ray Chandler_, May 19 2008