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a(1)=1; for n>1, a(n) = largest prime divisor of n!!.
8

%I #8 Feb 15 2014 20:39:42

%S 1,2,3,2,5,3,7,3,7,5,11,5,13,7,13,7,17,7,19,7,19,11,23,11,23,13,23,13,

%T 29,13,31,13,31,17,31,17,37,19,37,19,41,19,43,19,43,23,47,23,47,23,47,

%U 23,53,23,53,23,53,29,59,29,61,31,61,31,61,31,67,31,67,31,71,31,73,37

%N a(1)=1; for n>1, a(n) = largest prime divisor of n!!.

%H Harvey P. Dale, <a href="/A139421/b139421.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = A006530(A006882(n)). - _Michel Marcus_, Nov 08 2013

%t a = {}; Do[b = First[Last[FactorInteger[n!! ]]]; AppendTo[a, b], {n, 2, 100}]; a

%t FactorInteger[#][[-1,1]]&/@(Range[80]!!) (* _Harvey P. Dale_, Feb 15 2014 *)

%Y Cf. A010693.

%K nonn

%O 1,2

%A _Artur Jasinski_, Apr 21 2008