A120791 - OEIS

A120791

Numerators of partial sums of Catalan numbers scaled by powers of -1/20.

1, 19, 191, 1527, 76357, 1527119, 15271223, 1221697411, 488678993, 244339494069, 2443394944889, 97735797766167, 977357977713673, 3909431910817547, 39094319108242331, 6255091057316833991

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OFFSET

0,2

COMMENTS

From the expansion of sqrt(1+1/5) = 1+(1/10)*sum(C(k)/(-20)^k,k=0..infinity) one has, with the partial sums r(n) are defined below, r:=limit(r(n),n to infinity)= (2*(sqrt(30)-5)) = 0.954451150....

Denominators are given under A120796.

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)/20^k,k=0..n) with C(k):=A000108(k) (Catalan numbers). Rationals r(n) are taken in lowest terms.

EXAMPLE

Rationals r(n): [1, 19/20, 191/200, 1527/1600, 76357/80000,

1527119/1600000, 15271223/16000000, 1221697411/1280000000,...]

CROSSREFS

Sequence in context: A142268 A107695 A005759 * A048556 A141995 A210339

Adjacent sequences: A120788 A120789 A120790 * A120792 A120793 A120794

KEYWORD

nonn,easy,frac

AUTHOR

Wolfdieter Lang, Jul 20 2006

STATUS

approved