OFFSET
1,1
COMMENTS
"At the end of Section 6, the sequences of numerators and denominators of R_n were considered. What do these sequences count? Further, is there some kind of combinatorial reciprocity [Beck] occurring here?" - [S. Northshield]
LINKS
Gheorghe Coserea, Table of n, a(n) for n = 1..54321
Matthias Beck, Combinatorial Reciprocity Theorems, arXiv:1201.2212 [math.CO], 2012.
S. Northshield, An Analogue of Stern's Sequence for Z[sqrt(2)], Journal of Integer Sequences, 18 (2015), #15.11.6.
Lionel Ponton, Two trees enumerating the positive rationals, arXiv:1707.02366 [math.NT], 2017. See tree p. 4.
Lionel Ponton, Two trees enumerating the positive rationals, Integers, Electronic Journal of Combinatorial Number Theory 18A (2018), #A17.
Lukas Spiegelhofer, A Digit Reversal Property for an Analogue of Stern's Sequence, Journal of Integer Sequences, Vol. 20 (2017), #17.10.8.
FORMULA
a(n) = numerator(R(n)), where R(n) = 4 * A007949(n) + 2 - 2/R(n-1), with R(1) = 2. - Gheorghe Coserea, Nov 11 2016
EXAMPLE
2, 1, 4, 3/2, 2/3, 3, 4/3, 1/2, 6, 5/3, 4/5, 7/2, 10/7, 3/5, 8/3, 5/4, 2/5, 5, 8/5, 3/4, ...
MATHEMATICA
R[1] = 2; R[n_] := R[n] = 4 IntegerExponent[n, 3] + 2 - 2/R[n-1];
Table[R[n] // Numerator, {n, 1, 100}] (* Jean-François Alcover, Sep 03 2018, after Gheorghe Coserea *)
PROG
(PARI)
seq(N) = {
my(v = vector(N)); v[1] = 2;
for (n = 2, N, v[n] = 4*valuation(n, 3) + 2 - 2 / v[n-1]);
return(v);
};
apply(numerator, seq(88)) \\ Gheorghe Coserea, Nov 11 2016
CROSSREFS
KEYWORD
nonn,frac
AUTHOR
N. J. A. Sloane, Nov 08 2016
EXTENSIONS
More terms from Gheorghe Coserea, Nov 11 2016
STATUS
approved