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Denominators of partial sums of the Madhava series for Pi/(2*sqrt(3)) = A093766.
1

%I #11 May 16 2022 04:58:04

%S 1,9,45,945,25515,280665,3648645,32837805,186080895,31819833045,

%T 286378497405,6586705440315,98800581604725,8002847109982725,

%U 232082566189499025,7194559551874469775,21583678655623409325,7194559551874469775,2395788330774198435075,21562094976967785915675

%N Denominators of partial sums of the Madhava series for Pi/(2*sqrt(3)) = A093766.

%C For a comment and references see A352397.

%F a(n) = denominator(Sum_{j=0..n} (-1)^j/((2*j+1)*3^j)), for n >= 0.

%t Denominator @ Accumulate @ Table[(-1)^j/((2*j + 1)*3^j), {j, 0, 20}] (* _Amiram Eldar_, Apr 08 2022 *)

%o (PARI) a(n) = denominator(sum(j=0, n, (-1)^j/((2*j+1)*3^j))); \\ _Michel Marcus_, Apr 08 2022

%Y Cf. A352397 (numerators).

%Y Cf. A093766.

%K nonn,frac,easy

%O 0,2

%A _Wolfdieter Lang_, Apr 07 2022