A130414 Denominators of partial sums for a series for Pi/3.

1, 18, 45, 1260, 945, 20790, 135135, 1081080, 765765, 87297210, 43648605, 4015671660, 5019589575, 30117537450, 436704293025, 216605329340400, 13537833083775, 27075666167550, 500899824099675, 2003599296398700

Offset: 0

Author

Wolfdieter Lang, Jun 01 2007

Keywords

• nonn
• frac
• easy

Comments

The numerators are given in A130413.

For the rationals r(n) see A130413 and the W. Lang link given there.

Links

• Robert Israel, Table of n, a(n) for n = 0..1000

Programs

Maple

f:= n -> denom(1+ (4/3)*add(((-1)^(j+1))/((2*j+1)*((2*j+1)^2-1)), j=1..n)):
map(f, [$0..20]);# Robert Israel, Jul 27 2015

Formula

a(n) = denominator(r(n)), n>=0, with the rationals defined in A130413.