A126289 - OEIS

%I #13 Oct 07 2020 05:38:54

%S 1,1,2,6,2,10,3,28,6,6,5,44,3,26,21,40,2,102,3,76,15,14,11,184,15,10,

%T 117,12,7,174,5,496,6,22,85,84,3,74,57,104,5,246,7,172,99,10,23,752,

%U 21,70,15,68,13,954,15,88,21,38,29,708,5,122,279,224,10,78,11,268,51,230,7

%N a(1) = 1, a(2) = 1, a(n) = n * LargestPrimeFactor(n-1) / LargestPrimeFactor(n).

%H Ivan Neretin, <a href="/A126289/b126289.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A006530(n-1)*A052126(n) for n>2. - _Michel Marcus_, May 20 2015

%e a(6) = 6 * LargestPrimeFactor(5) / LargestPrimeFactor(6) = 6 * 5 / 3 = 10

%t a[1] := 1; a[2] := 1; a[n_] := n*FactorInteger[n - 1][[-1, 1]]/FactorInteger[n][[-1, 1]]; Table[a[n], {n, 71}] (* _Ivan Neretin_, May 20 2015 *)

%o (PARI) gpf(n) = vecmax(factor(n)[,1]); \\ A006530

%o a(n) = if (n<=2, 1, n*gpf(n-1)/gpf(n)); \\ _Michel Marcus_, Oct 07 2020

%Y Cf. A126286, A126287, A126288, A006530.

%K easy,nonn

%O 1,3

%A _Lior Manor_, Dec 25 2006