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%I #26 May 23 2024 16:13:39
%S 1,11,53,67,109,121,137,151,179,193,263,277,347,389,431,487,557,571,
%T 583,599,613,641,683,737,739,809,823,907,977,991,1019,1033,1061,1103,
%U 1117,1187,1199,1201,1229,1327,1331,1439,1453,1481,1507,1523,1579,1607,1621
%N Divisible only by primes congruent to 4 mod 7.
%C a(1) = 1 is included by convention (all the primes that divide 1 are congruent to 4 mod 7).
%H Vincenzo Librandi, <a href="/A004622/b004622.txt">Table of n, a(n) for n = 1..1000</a>
%t ok[1]=True;ok[n_]:=And@@(Mod[#,7]==4&)/@FactorInteger[n][[All,1]];Select[Range[5000],ok] (* _Vincenzo Librandi_, Aug 20 2012 *)
%t Join[{1},Select[Range[2000],Union[Mod[FactorInteger[#][[;;,1]],7]]=={4}&]] (* _Harvey P. Dale_, May 04 2023 *)
%o (Magma) [n: n in [1..2000] | forall{d: d in PrimeDivisors(n) | d mod 7 eq 4}]; // _Vincenzo Librandi_, Aug 20 2012
%K nonn
%O 1,2
%A _N. J. A. Sloane_
%E Offset changed from 0 to 1 by _Vincenzo Librandi_, Aug 20 2012
%E Missing a(41) added by _Sean A. Irvine_, Jun 08 2016
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