A220096 a(1)=0, n-1 if n is prime, else largest proper divisor of n.

0, 1, 2, 2, 4, 3, 6, 4, 3, 5, 10, 6, 12, 7, 5, 8, 16, 9, 18, 10, 7, 11, 22, 12, 5, 13, 9, 14, 28, 15, 30, 16, 11, 17, 7, 18, 36, 19, 13, 20, 40, 21, 42, 22, 15, 23, 46, 24, 7, 25, 17, 26, 52, 27, 11, 28, 19, 29, 58, 30, 60, 31, 21, 32, 13, 33, 66, 34, 23, 35, 70

Offset: 1

Author

Jon Perry, Dec 04 2012

Keywords

• nonn

Comments

On the dual isomorphism [n, n*] this function represents n* - see A091934.

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A032742, A091934.

Programs

Haskell

a220096 n = if z == 1 then n - 1 else z  where z = a032742 n
-- Reinhard Zumkeller, Nov 23 2014

Mathematica

Join[{0}, Table[If[PrimeQ[n], n - 1, Divisors[n][[-2]]], {n, 2, 100}]] (* T. D. Noe, Dec 04 2012 *)

PARI

a(n) = if (n==1, 0, isprime(n), n-1, my(d=divisors(n)); d[#d-1]); \\ Michel Marcus, Dec 24 2017

Formula

a(n) = if A220096(n) = 1 then n - 1 else A220096(n). - Reinhard Zumkeller, Nov 23 2014