A099634 - OEIS

%I #9 Oct 19 2019 03:20:28

%S 4,3,4,5,1,7,4,3,1,11,1,13,1,1,4,17,1,19,1,1,1,23,1,5,1,3,1,29,1,31,4,

%T 1,1,1,1,37,1,1,1,41,1,43,1,1,1,47,1,7,1,1,1,53,1,1,1,1,1,59,1,61,1,1,

%U 4,1,1,67,1,1,1,71,1,73,1,1,1,1,1,79,1,3,1,83,1,1,1,1,1,89,1,1,1,1,1,1,1,97

%N a(n) = gcd(P+p, P*p) where P is the largest and p the smallest prime factor of n.

%e If n is prime q > 2, then a(n) = gcd(q^2, 2q) = q.

%t PrimeFactors[n_Integer] := Flatten[ Table[ # [[1]], {1}] & /@ FactorInteger[n]]; f[n_] := Block[{pf = PrimeFactors[n]}, GCD[pf[[1]] + pf[[ -1]], pf[[1]]*pf[[ -1]] ]]; Table[ f[n], {n, 2, 97}] (* _Robert G. Wilson v_, Nov 04 2004 *)

%K nonn

%O 2,1

%A _Labos Elemer_, Oct 28 2004