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URL: https://oeis.org/A046666

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A046666
a(n) = n - (smallest prime dividing n).
10
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
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
Sequence in context: A144775 A249744 A245075 * A276093 A176296 A382014
KEYWORD
nonn
STATUS
approved