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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 (list; graph; refs; listen; history; text; internal format)
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

Ivan Neretin, Table of n, a(n) for n = 1..4097

Alexander Bogomolny, Cut-the-knot on Stern-Brocot trees

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: A210751 A279791 A132886 * A070871 A096115 A289838

Adjacent sequences:  A119269 A119270 A119271 * A119273 A119274 A119275

KEYWORD

nonn,tabf

AUTHOR

Joshua Zucker, May 11 2006

STATUS

approved

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Last modified April 21 22:12 EDT 2019. Contains 322328 sequences. (Running on oeis4.)