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 A097704 Elements of A097703 not of form 3k + 1. 4

%I

%S 12,24,60,62,84,87,122,137,144,162,171,180,212,237,264,269,287,302,

%T 312,318,362,387,416,420,422,423,437,462,465,480,512,537,563,587,591,

%U 612,662,665,684,687,710,722,737,759,762,786,812,837,840,857,887,902

%N Elements of A097703 not of form 3k + 1.

%C Conjecture: "most" of the terms also belong to [(A067778-1)/2]. Exceptions are {302, 2117, ...}. In other words, most terms satisfy: GCD(2n+1, numerator(B(4n+2))) is not squarefree, with B(n) the Bernoulli numbers.

%t usigma[n_] := Block[{d = Divisors[n]}, Plus @@ Select[d, GCD[ #, n/# ] == 1 &]]; Complement[ Range[1017], Table[3k - 2, {k, 340}], (Select[ Range[220000], DivisorSigma[1, # ] == 2usigma[ # ] &] - 108)/216] (* _Robert G. Wilson v_, Aug 28 2004 *)

%K nonn

%O 1,1

%A _Ralf Stephan_, Aug 26 2004

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Last modified December 1 13:38 EST 2021. Contains 349429 sequences. (Running on oeis4.)