A046666 a(n) = n - (smallest prime dividing n).

0, 0, 2, 0, 4, 0, 6, 6, 8, 0, 10, 0, 12, 12, 14, 0, 16, 0, 18, 18, 20, 0, 22, 20, 24, 24, 26, 0, 28, 0, 30, 30, 32, 30, 34, 0, 36, 36, 38, 0, 40, 0, 42, 42, 44, 0, 46, 42, 48, 48, 50, 0, 52, 50, 54, 54, 56, 0, 58, 0, 60, 60, 62, 60, 64, 0, 66, 66, 68, 0, 70, 0

Offset

2,3

Comments

From Reinhard Zumkeller, Jul 08 2010: (Start)

a(n)=0 iff n is not composite;

for composite n: a(n) = max(m: m < n and gcd(m,n) > 1). (End)

Links

Antti Karttunen, Table of n, a(n) for n = 2..16385

Formula

a(n) = n - A020639(n). - Michel Marcus, Jan 07 2015

Maple

with(numtheory):
a:= n-> n-min(factorset(n)[]):
seq(a(n), n=2..100);  # Alois P. Heinz, Jan 07 2015

Mathematica

Table[n-First@(First/@FactorInteger[n]), {n, 2, 200}] (* Vladimir Joseph Stephan Orlovsky, Apr 08 2011 *)

Prog

(PARI) a(n) = n - factor(n)[1, 1]; \\ Michel Marcus, Jan 07 2015

Crossrefs

Cf. A020639, A061228.

Sequence in context: A144775 A249744 A245075 * A276093 A176296 A349232

Adjacent sequences: A046663 A046664 A046665 * A046667 A046668 A046669

Keyword

nonn

Author

N. J. A. Sloane

Status

approved