A099634 a(n) = gcd(P+p, P*p) where P is the largest and p the smallest prime factor of n.

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, 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, 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

Offset: 2

Author

Labos Elemer, Oct 28 2004

Keywords

• nonn

Examples

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

Programs

Mathematica

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 *)