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A097704 Elements of A097703 not of form 3k + 1. 4
12, 24, 60, 62, 84, 87, 122, 137, 144, 162, 171, 180, 212, 237, 264, 269, 287, 302, 312, 318, 362, 387, 416, 420, 422, 423, 437, 462, 465, 480, 512, 537, 563, 587, 591, 612, 662, 665, 684, 687, 710, 722, 737, 759, 762, 786, 812, 837, 840, 857, 887, 902 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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.

LINKS

Table of n, a(n) for n=1..52.

MATHEMATICA

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 *)

CROSSREFS

Sequence in context: A247944 A346865 A123980 * A289132 A098585 A087105

Adjacent sequences:  A097701 A097702 A097703 * A097705 A097706 A097707

KEYWORD

nonn

AUTHOR

Ralf Stephan, Aug 26 2004

STATUS

approved

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Last modified October 22 16:15 EDT 2021. Contains 348174 sequences. (Running on oeis4.)