A004623 - OEIS

%I #11 Oct 26 2023 00:44:02

%S 1,5,19,25,47,61,89,95,103,125,131,173,229,235,257,271,305,313,361,

%T 383,397,439,445,467,475,509,515,523,593,607,625,655,677,691,719,733,

%U 761,859,865,887,893,929,971,1013

%N Divisible only by primes congruent to 5 mod 7.

%H Vincenzo Librandi, <a href="/A004623/b004623.txt">Table of n, a(n) for n = 1..1000</a>

%t  ok[1]=True;ok[n_]:=And@@(Mod[#,7]==5&)/@FactorInteger[n][[All,1]];Select[Range[5000],ok] (* _Vincenzo Librandi_, Aug 20 2012 *)

%o (Magma) [n: n in [1..2000] | forall{d: d in PrimeDivisors(n) | d mod 7 eq 5}]; // _Vincenzo Librandi_, Aug 20 2012

%K nonn

%O 1,2

%A _N. J. A. Sloane_