A100951 - OEIS

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A100951

Number of ways to write n = p*q + r with three distinct primes p, q and r.

6

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 2, 0, 0, 0, 4, 0, 2, 0, 1, 1, 3, 0, 3, 2, 3, 1, 4, 0, 2, 2, 3, 2, 3, 0, 5, 4, 3, 2, 5, 0, 4, 3, 5, 4, 3, 1, 4, 3, 5, 4, 6, 1, 3, 4, 6, 6, 4, 0, 3, 7, 6, 5, 6, 1, 6, 6, 6, 4, 4, 3, 4, 7, 7, 6, 6, 2, 6, 7, 8, 8, 3, 2, 7, 6, 7, 8, 8, 1, 4, 7, 10, 10, 6, 6, 7, 10, 9, 8, 5, 5, 5, 8

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OFFSET

1,13

COMMENTS

a(n)<=A100950(n)<=A100949(n)<=Min{A000720(n), A072000(n)}.

a(n) = A000040(i) + A006881(j) for some i and j, such that A000040(i) is not a factor of A006881(j);

a(A100952(n)) = 0.

a(A160373(n)) = n and a(m) <> n for m < A160373(n). [From Reinhard Zumkeller, May 11 2009]

LINKS

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

EXAMPLE

A100949(21) = #{7+2*7, 11+2*5, 17+2*2} = 3,

a(21) = #{11+2*5} = 1.

CROSSREFS

Sequence in context: A113277 A114855 A221381 * A348616 A348613 A285182

Adjacent sequences: A100948 A100949 A100950 * A100952 A100953 A100954

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Nov 23 2004

STATUS

approved