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A127750 Row sums of inverse of number triangle A(n,k) = 1/(2n+1) if k <= n <= 2k, 0 otherwise. 3
1, 3, 2, 5, 2, 4, 2, 7, 2, 4, 2, 6, 2, 4, 2, 9, 2, 4, 2, 6, 2, 4, 2, 8, 2, 4, 2, 6, 2, 4, 2, 11, 2, 4, 2, 6, 2, 4, 2, 8, 2, 4, 2, 6, 2, 4, 2, 10, 2, 4, 2, 6, 2, 4, 2, 8, 2, 4, 2, 6, 2, 4, 2, 13, 2, 4, 2, 6, 2, 4, 2, 8, 2, 4, 2, 6, 2, 4, 2, 10, 2, 4, 2, 6, 2, 4, 2, 8, 2, 4, 2, 6, 2, 4, 2, 12, 2, 4, 2, 6, 2, 4, 2, 8, 2, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Row sums of A127749.

Conjecture: a(n) mod 2 gives Fredholm-Rueppel sequence A036987.

The conjecture is true at least up to n=2048. - Antti Karttunen, Sep 29 2018

LINKS

Antti Karttunen, Table of n, a(n) for n = 0..2048

MATHEMATICA

A[n_, k_] := If[k <= n <= 2k, 1/(2n+1), 0];

Total /@ Inverse[Array[A, {128, 128}, {0, 0}]] (* Jean-Fran├žois Alcover, Feb 10 2021 *)

PROG

(PARI)

up_to = 128;

A127750aux(n, k) = if(k<=n, if(n<=(2*k), 1/(n+n+1), 0), 0);

A127750list(up_to) = { my(m1=matrix(up_to, up_to, n, k, A127750aux(n-1, k-1)), m2 = matsolve(m1, matid(up_to)), v = vector(up_to)); for(n=1, up_to, v[n] = vecsum(m2[n, ])); (v); };

v127750 = A127750list(1+up_to);

A127750(n) = v127750[1+n]; \\ Antti Karttunen, Sep 29 2018

CROSSREFS

Cf. A127749, A127752.

Sequence in context: A231146 A287692 A208889 * A112528 A154421 A057034

Adjacent sequences:  A127747 A127748 A127749 * A127751 A127752 A127753

KEYWORD

nonn

AUTHOR

Paul Barry, Jan 28 2007

EXTENSIONS

More terms from Antti Karttunen, Sep 29 2018

STATUS

approved

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Last modified October 16 05:41 EDT 2021. Contains 348035 sequences. (Running on oeis4.)