|
%I #13 Dec 19 2020 10:35:47
%S 3,5,7,3,11,13,7,17,19,7,23,5,13,29,31,11,17,37,19,41,43,11,47,7,17,
%T 53,11,19,59,61,31,13,67,23,71,73,37,19,79,5,83,17,43,89,13,31,47,97,
%U 11,101,103,13,107,109,37,113,23,29,59,11,61,31,127,43,131,19
%N Greatest prime factor of n and 2*n+1
%H Harvey P. Dale, <a href="/A199423/b199423.txt">Table of n, a(n) for n = 1..1000</a>
%F a(n) = A006530(A014105(n)).
%t Table[Max[Flatten[FactorInteger[{n,2 n+1}],1][[All,1]]],{n,70}] (* _Harvey P. Dale_, Mar 25 2020 *)
%o (PARI) gpf(n)=local(ps);if(n<2,n,ps=factor(n)[,1]~;ps[#ps])
%o vector(80,n,gpf(n*(2*n+1)))
%Y Cf. A006530, A014105, A074399, A093074, A076605.
%K nonn,easy
%O 1,1
%A _Franklin T. Adams-Watters_, Nov 06 2011
|
