A004619 - OEIS

%I #18 Oct 26 2023 00:42:26

%S 1,29,43,71,113,127,197,211,239,281,337,379,421,449,463,491,547,617,

%T 631,659,673,701,743,757,827,841,883,911,953,967,1009,1051,1093,1163,

%U 1247,1289,1303,1373,1429,1471

%N Numbers divisible only by primes congruent to 1 mod 7.

%H Vincenzo Librandi, <a href="/A004619/b004619.txt">Table of n, a(n) for n = 1..1000</a>

%t ok[1]=True;ok[n_]:=And@@(Mod[#,7]==1&)/@FactorInteger[n][[All,1]];Select[Range[6000],ok] (* _Vincenzo Librandi_, Aug 20 2012 *)

%o (Magma) [n: n in [1..2000] | forall{d: d in PrimeDivisors(n) | d mod 7 eq 1}]; // _Vincenzo Librandi_, Aug 20 2012

%o (PARI) is(n)=if(n%7!=1, return(0)); my(f=factor(n)[,1]); for(i=1,#f~, if(f[i]%7!=1, return(0))); 1 \\ _Charles R Greathouse IV_, Jul 02 2016

%K nonn,easy

%O 1,2

%A _N. J. A. Sloane_