A071219 Numbers m such that the largest prime factor of prime(m) + prime(m+1) equals m.

2, 3, 439

Offset: 1

Author

Labos Elemer, May 17 2002

Keywords

• nonn
• bref
• more

Comments

a(4), if it exists, is larger than 10^7.

a(4) > 5*10^14, if it exists. - Giovanni Resta, Jul 14 2018

Examples

			Numbers x such that A006530(A001043(x)) = x.
x = 2 is a term: p(2) + p(3) = 3 + 5 = 8 with largest factor = 2 = x.
x = 3 is a term: p(3) + p(4) = 5 + 7 = 12 with largest factor = 3 = x.
x = 439 is a term: p(439) + p(440) = 3067 + 3079 = 6146 = 2*7*439 = 14x.
		

Crossrefs

Cf. A006530, A001043, A071216-A071218.

Programs

Mathematica

DeleteCases[#, 0] &@ MapIndexed[Boole[#1 == First@ #2] First@ #2 &, Map[FactorInteger[Total@ #][[-1, 1]] &, Partition[Prime@ Range[10^6], 2, 1]]] (* Michael De Vlieger, Aug 09 2017 *)

Extensions

Edited by N. J. A. Sloane, Aug 09 2017