A126289 a(1) = 1, a(2) = 1, a(n) = n * LargestPrimeFactor(n-1) / LargestPrimeFactor(n).

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, 117, 12, 7, 174, 5, 496, 6, 22, 85, 84, 3, 74, 57, 104, 5, 246, 7, 172, 99, 10, 23, 752, 21, 70, 15, 68, 13, 954, 15, 88, 21, 38, 29, 708, 5, 122, 279, 224, 10, 78, 11, 268, 51, 230, 7

Offset: 1

Author

Lior Manor, Dec 25 2006

Keywords

• easy
• nonn

Examples

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

Links

• Ivan Neretin, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A126286, A126287, A126288, A006530.

Programs

Mathematica

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 *)

PARI

gpf(n) = vecmax(factor(n)[,1]); \\ A006530
a(n) = if (n<=2, 1, n*gpf(n-1)/gpf(n)); \\ Michel Marcus, Oct 07 2020

Formula

a(n) = A006530(n-1)*A052126(n) for n>2. - Michel Marcus, May 20 2015