A174981 Numerators of the L-tree, left-to-right enumeration.

0, 1, 1, 2, 3, 1, 2, 3, 5, 2, 5, 3, 4, 1, 3, 4, 7, 3, 8, 5, 7, 2, 7, 5, 8, 3, 7, 4, 5, 1, 4, 5, 9, 4, 11, 7, 10, 3, 11, 8, 13, 5, 12, 7, 9, 2, 9, 7, 12, 5, 13, 8, 11, 3, 10, 7, 11, 4, 9, 5, 6, 1, 5, 6, 11, 5, 14, 9, 13, 4, 15, 11, 18, 7, 17, 10, 13, 3, 14, 11, 19, 8, 21, 13, 18, 5, 17, 12, 19, 7, 16

Offset

0,4

Comments

a(n) is a subsequence of A174980. a(n)/A002487(n+2) enumerates all the reduced nonnegative rational numbers exactly once (L-tree).

Links

Table of n, a(n) for n=0..90.

Edsger Dijkstra, Selected Writings on Computing, Springer, 1982, p. 232. EWD 578: More about the function fusc.

Peter Luschny, Rational Trees and Binary Partitions.

Moritz A. Stern, Über eine zahlentheoretische Funktion, J. Reine Angew. Math., 55 (1858), 193-220.

Example

The sequence splits into rows of length 2^k:
0,
1, 1,
2, 3, 1, 2,
3, 5, 2, 5, 3, 4, 1, 3,
4, 7, 3, 8, 5, 7, 2, 7, 5, 8, 3, 7, 4, 5, 1, 4,
...
The fractions are
0/1,
1/2, 1/1,
2/3, 3/2, 1/3, 2/1,
3/4, 5/3, 2/5, 5/2, 3/5, 4/3, 1/4, 3/1,
4/5, 7/4, 3/7, 8/3, 5/8, 7/5, 2/7, 7/2, 5/7, 8/5, 3/8, 7/3, 4/7, 5/4, 1/5, 4/1,
...

Maple

SternDijkstra := proc(L, p, n) local k, i, len, M; len := nops(L); M := L; k := n; while k > 0 do M[1+(k mod len)] := add(M[i], i = 1..len); k := iquo(k, len); od; op(p, M) end:
Ltree := proc(n) 5*2^ilog2(n+1); SternDijkstra([0, 1], 1, n + 2 + %) / SternDijkstra([1, 0], 2, n + 2) end:
a := proc(n) 5*2^ilog2(n+1); SternDijkstra([0, 1], 1, n + 2 + %) end:
seq(a(n), n=0..90);

Mathematica

SternDijkstra[L_, p_, n_] := Module[{k, i, len, M}, len := Length[L]; M = L; k = n; While[k > 0, M[[1 + Mod[k, len]]] = Sum[M[[i]], {i, 1, len}]; k = Quotient[k, len]]; M[[p]]]; Ltree[n_] := With[{k = 5*2^Simplify[ Floor[ Log[2, n + 1]]]}, SternDijkstra[{0, 1}, 1, n + 2 + k]/ SternDijkstra[{1, 0}, 2, n + 2]]; a[0] = 0; a[n_] := With[{k = 5*2^Simplify[ Floor[ Log[2, n + 1]]]}, SternDijkstra[{1, 0}, 1, n + 2 + k]]; row[0] = {a[0]}; row[n_] := Table[a[k], {k, 2^n - 3, 2^(n+1) - 4}] // Reverse; Table[row[n], {n, 0, 6}] // Flatten (* Jean-François Alcover, Jul 26 2013, after Maple *)

Crossrefs

Cf. A002487, A070879, A047679, A007306, A174980.

Sequence in context: A076645 A350604 A011448 * A067280 A167157 A238837

Adjacent sequences: A174978 A174979 A174980 * A174982 A174983 A174984

Keyword

easy,nonn,frac,tabf

Author

Peter Luschny, Apr 03 2010

Status

approved