A071219 Numbers m such that the largest prime factor of prime(m) + prime(m+1) equals m.
2, 3, 439
Offset: 1
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.
Programs
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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
Comments