A176257 - OEIS

%I #12 Nov 27 2019 05:32:06

%S 15,39,51,75,87,91,111,119,123,135,143,159,183,187,195,203,219,255,

%T 259,267,287,291,303,319,327,339,351,371,375,407,411,427,435,447,451,

%U 455,459,471,507,511,519,543,551,555,579,583,591,595,615,623,663,667,671

%N Numbers of the form 4k-1 with greatest prime divisor of the form 4m+1.

%C By definition, all terms are composite numbers.

%H Amiram Eldar, <a href="/A176257/b176257.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[4*Range[200]-1,Divisible[FactorInteger[#][[-1,1]]-1,4]&] (* _Harvey P. Dale_, May 17 2013 *)

%o (PARI) isok(n) = ((n % 4) == 3) && ((vecmax(factor(n)[,1]) % 4) == 1); \\ _Michel Marcus_, Feb 07 2016

%Y Cf. A176256, A176255, A002148, A002145, A016813, A004767.

%K nonn

%O 1,1

%A _Vladimir Shevelev_, Apr 13 2010

%E Corrected and extended by _Harvey P. Dale_, May 17 2013