A373506 Decimal expansion of 4*Pi/3^(3/2) - Pi^2/9.

1, 3, 2, 1, 7, 7, 6, 4, 4, 1, 0, 8, 0, 1, 3, 9, 5, 0, 9, 8, 1, 0, 4, 9, 4, 2, 3, 2, 4, 2, 5, 5, 2, 4, 1, 8, 3, 5, 6, 6, 1, 2, 1, 7, 2, 9, 9, 8, 5, 7, 8, 8, 4, 7, 5, 6, 0, 2, 8, 0, 7, 7, 6, 0, 9, 3, 7, 4, 9, 2, 5, 9, 4, 5, 6, 6, 3, 3, 7, 9, 2, 9, 0, 2, 3, 0, 8

Offset

1,2

Links

Table of n, a(n) for n=1..87.

Renzo Sprugnoli, Sums of reciprocals of the central binomial coefficients, INTEGERS 6 (2006) #A27.

Formula

Equals Sum_{n>=0} 1/((n+1)*binomial(2n,n)).

The alternating case is Sum_{n>=0} (-1)^n/((n+1)*binomial(2*n,n)) = 8*log(phi)/sqrt(5)-4*log^2(phi) = 0.79537... where phi is the golden ratio.

Equals A275486 - A100044. - Stefano Spezia, Jun 07 2024

Example

1.321776441080139509810494232425524183566...

Maple

4*Pi/3^(3/2)-Pi^2/9 ; evalf(%) ;

Mathematica

RealDigits[4*Pi/3^(3/2) - Pi^2/9, 10, 120][[1]] (* Amiram Eldar, Jun 10 2024 *)

Prog

(PARI) 4*Pi/3^(3/2) - Pi^2/9 \\ Amiram Eldar, Jun 10 2024

Crossrefs

Cf. A100044, A275486, A073016 (no n+1 denominator), A073010 (denominator n), A373507 (denominator n-1).

Sequence in context: A161009 A111960 A130462 * A059380 A145035 A359413

Adjacent sequences: A373503 A373504 A373505 * A373507 A373508 A373509

Keyword

cons,nonn

Author

R. J. Mathar, Jun 07 2024

Status

approved