A100951 Number of ways to write n = p*q + r with three distinct primes p, q and r.

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

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