A079084 Greatest prime factor of (prime(n)+1)*(prime(n+1)+1)/4.

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, 19, 19, 11, 23, 23, 7, 19, 79, 79, 41, 29, 29, 13, 13, 97, 97, 11, 53, 53, 19, 23, 23, 13, 11, 11, 43, 43, 11, 17, 139, 139, 71, 71, 11, 13, 157, 157, 83, 83, 29, 29, 59, 59, 23, 23, 19

Offset: 1

Author

Reinhard Zumkeller, Dec 22 2002

Keywords

• nonn
• nice

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A006530, A079079.

Programs

Haskell

a079084 = a006530 . a079079  -- Reinhard Zumkeller, Oct 08 2012

Mathematica

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

PARI

a(n) = my(f=factor((prime(n)+1)*(prime(n+1)+1)/4)); f[#f~,1]; \\ Michel Marcus, Nov 12 2023

Formula

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