A120995 Denominators of rationals related to John Wallis' product formula for Pi/2 (from his 'Arithmetica infinitorum' from 1659).

1, 15, 175, 3675, 14553, 231231, 920205, 234652275, 2807136475, 14933966047, 59612442981, 11425718238025, 15211755050625, 243077636829375, 971230202264925, 993568496917018275, 3970836034391543625

Offset: 1

Author

Wolfdieter Lang, Aug 01 2006

Keywords

• nonn
• easy
• frac

Comments

The corresponding numerators are A120994.

The rationals W(n):= (((4^n)/binomial(2*n,n))^2)/(2*n+1) converge to Pi/2 = 1.570796327...

Formula

a(n) = denominators((3/4)*W(n)), n>=1.