A120794 Numerators of partial sums of Catalan numbers scaled by powers of -1/16.

1, 15, 121, 3867, 30943, 495067, 3960569, 253475987, 2027808611, 32444935345, 259559486959, 8305903553295, 66447228478363, 1063155655468083, 8505245244078969, 1088671391232413187

Offset

0,2

Comments

From the expansion of sqrt(1+1/4) = 1+(1/8)*sum(C(k)/(-16)^k,k=0..infinity) one has, with the partial sums r(n) are defined below, r:=limit(r(n),n to infinity)= 4*(sqrt(5)-2) = 4*(2*phi-3)) = 0.944271909...

Denominators coincide with the listed numbers of A120785 but may differ for higher n values.

This is the first member (p=1) of the fourth famliy of scaled Catalan sums with limits in Q(sqrt(5)). See the W. Lang link under A120996.

Links

Table of n, a(n) for n=0..15.

W. Lang: Rationals r(n) and limit.

Formula

a(n)=numerator(r(n)), with the rationals r(n):=sum(((-1)^k)*C(k)/16^k,k=0..n) with C(k):=A000108(k) (Catalan numbers). Rationals r(n) are taken in lowest terms.

Example

Rationals r(n): [1, 15/16, 121/128, 3867/4096, 30943/32768,
495067/524288, 3960569/4194304,...].

Crossrefs

The second member (p=2) of this p-family is A121012/A121013.

Sequence in context: A138424 A279267 A357602 * A264377 A038743 A181377

Adjacent sequences: A120791 A120792 A120793 * A120795 A120796 A120797

Keyword

nonn,easy,frac

Author

Wolfdieter Lang, Jul 20 2006

Status

approved