login
A119272
Product of numerator and denominator in Stern-Brocot tree.
2
0, 0, 1, 2, 2, 3, 6, 6, 3, 4, 10, 15, 12, 12, 15, 10, 4, 5, 14, 24, 21, 28, 40, 35, 20, 20, 35, 40, 28, 21, 24, 14, 5, 6, 18, 33, 30, 44, 65, 60, 36, 45, 84, 104, 77, 70, 88, 63, 30, 30, 63, 88, 70, 77, 104, 84, 45, 36, 60, 65, 44, 30, 33, 18, 6, 7, 22, 42, 39, 60, 90, 85, 52, 70
OFFSET
1,4
COMMENTS
The sum of the reciprocals of each row (n > 0) is 1 (i.e., 1/1, 1/2 + 1/2, 1/3 + 1/6 + 1/6 + 1/3, 1/4 + ... + 1/4, 1/5 + ... + 1/5, ...). The cut-the-knot link gives credit to Pierre Lamothe for this observation.
LINKS
FORMULA
Take each row of A049449 and append its reverse.
Also, a(n) = A007305(n-1)*A047679(n-3) for n>=3.
CROSSREFS
Cf. A049449 (has the first half of each row), A007305 (numerators), A047679 (denominators).
Sequence in context: A328744 A345706 A132886 * A308483 A070871 A096115
KEYWORD
nonn,tabf
AUTHOR
Joshua Zucker, May 11 2006
STATUS
approved