This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A004621 #14 Oct 26 2023 00:43:09
%S A004621 1,3,9,17,27,31,51,59,73,81,93,101,153,157,177,199,219,227,241,243,
%T A004621 269,279,283,289,303,311,353,367,409,459,471,479,521,527,531,563,577,
%U A004621 597,619,647,657,661,681,723,729,773,787,807,829,837,849,857,867,909,933
%N A004621 Divisible only by primes congruent to 3 mod 7.
%H A004621 Vincenzo Librandi, <a href="/A004621/b004621.txt">Table of n, a(n) for n = 1..1000</a>
%t A004621 ok[1]=True;ok[n_]:=And@@(Mod[#,7]==3&)/@FactorInteger[n][[All,1]];Select[Range[3000],ok] (* _Vincenzo Librandi_, Aug 20 2012 *)
%o A004621 (Magma) [n: n in [1..1000] | forall{d: d in PrimeDivisors(n) | d mod 7 eq 3}]; // _Vincenzo Librandi_, Aug 20 2012
%Y A004621 Cf. A045437 (divisors).
%K A004621 nonn
%O A004621 1,2
%A A004621 _N. J. A. Sloane_
%E A004621 Offset changed from 0 to 1 by _Vincenzo Librandi_, Aug 20 2012