A079084 - OEIS

%I #21 Nov 12 2023 11:33:28

%S 3,3,3,3,7,7,5,5,5,5,19,19,11,11,3,5,31,31,17,37,37,7,7,7,17,17,13,11,

%T 19,19,11,23,23,7,19,79,79,41,29,29,13,13,97,97,11,53,53,19,23,23,13,

%U 11,11,43,43,11,17,139,139,71,71,11,13,157,157,83,83,29,29,59,59,23,23,19

%N Greatest prime factor of (prime(n)+1)*(prime(n+1)+1)/4.

%H Reinhard Zumkeller, <a href="/A079084/b079084.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = A006530(A079079(n)).

%t a[n_]:=FactorInteger[(Prime[n]+1)(Prime[n+1]+1)/4][[-1,1]]; Table[a[n],{n,1,74}] (* _Jean-François Alcover_, Mar 18 2011 *)

%t FactorInteger[(First[#]+1) (Last[#]+1)/4][[-1,1]]&/@Partition[Prime[ Range[100]],2,1] (* _Harvey P. Dale_, Nov 14 2011 *)

%o (Haskell)

%o a079084 = a006530 . a079079  -- _Reinhard Zumkeller_, Oct 08 2012

%o (PARI) a(n) = my(f=factor((prime(n)+1)*(prime(n+1)+1)/4)); f[#f~,1]; \\ _Michel Marcus_, Nov 12 2023

%Y Cf. A006530, A079079.

%K nonn,nice

%O 1,1

%A _Reinhard Zumkeller_, Dec 22 2002