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 A071821 #21 May 04 2022 06:53:00 %S A071821 5,10,13,15,17,20,25,26,29,30,34,37,39,40,41,45,50,51,52,53,58,60,61, %T A071821 65,68,73,74,75,78,80,82,85,87,89,90,91,97,100,101,102,104,106,109, %U A071821 111,113,116,117,119,120,122,123,125,130,135,136,137,143,145,146,148,149 %N A071821 Numbers whose largest prime factor is of the form 4k+1. %C A071821 Subsequence of A009003. - _M. F. Hasler_, Feb 06 2009 %H A071821 Robert Israel, <a href="/A071821/b071821.txt">Table of n, a(n) for n = 1..10000</a> %F A071821 Numbers k such that A006530(k) == 1 (mod 4). %p A071821 filter:= proc(n) %p A071821 max(numtheory:-factorset(n)) mod 4 = 1 %p A071821 end proc: %p A071821 select(filter, [$1..200]); # _Robert Israel_, Sep 11 2020 %t A071821 Select[Range[2, 150], Mod[FactorInteger[#][[-1,1]], 4] == 1 &] (* _Amiram Eldar_, May 04 2022 *) %o A071821 (PARI) for(n=2, 200, if((component(component(factor(n), 1), omega(n))-1)%4==0, print1(n, ", "))) %o A071821 (PARI) for( n=2,99, vecmax(factor(n)[,1])%4==1 && print1(n",")) \\ _M. F. Hasler_, Feb 06 2009 %Y A071821 Cf. A004431, A006530, A009000, A009003, A073503, A083025. %K A071821 easy,nonn %O A071821 1,1 %A A071821 _Benoit Cloitre_, Jun 07 2002