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%I #24 Sep 12 2019 10:47:28
%S 2,6,9,12,15,18,19,21,24,27,30,33,34,36,39,40,42,45,48,49,51,54,57,60,
%T 61,63,64,66,69,72,75,78,79,81,82,84,87,90,93,94,96,99,102,105,106,
%U 108,109,111,112,114,117,120,123,124
%N Numbers n such that the least prime factor of 2n - 3 is less than that of 2n - 1, unless 2n - 3 and 2n - 1 are (twin) primes.
%C Integers > 1 for which 2n - 3 is not in A001359 and A020639(2n-3) < A020639(2n-1).
%C Every multiple of 3 greater than 3 is in the sequence.
%H Amiram Eldar, <a href="/A173978/b173978.txt">Table of n, a(n) for n = 1..1000</a>
%e a(3) = 9 because 2*9 - 3 = 15, the least prime factor of which is 3 and that is smaller than the least prime factor of 2*9 - 1 = 17.
%t Select[Range[200], Not[PrimeQ[2# - 3] && PrimeQ[2# - 1]] && TrueQ[FactorInteger[2# - 3][[1, 1]] < FactorInteger[2# - 1][[1, 1]]] &] (* _Alonso del Arte_, Jun 05 2011 *)
%Y Cf. A020639, A001359, A173977.
%K nonn
%O 1,1
%A _Vladimir Shevelev_, Mar 04 2010
%E More terms from _Alonso del Arte_, Jun 05 2011
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