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 A280812 Numerators of 4 * Sum_{k=0..3*n-1} (-1)^k/(2*k+1) + (-1)^(n+1) * Sum_{k=0..2*n-1} (-1)^k/(2^(2*n-k-2) * (8*n-k-1) * binomial(8*n-k-2, 4*n+k)). 2
 22, 47171, 431302721, 741269838109, 26856502742629699, 211938730834003723543, 506119433541064524255449, 19809071774292917047896724979, 23285066731814401580687501596643, 89293478252053341114758995682016773 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 1/(2^(2*n-1) * (8*n+1) * binomial(8*n, 4*n)) < 1/2^(2*n-2) * Integral_{x=0..1} (x^(4*n) * (1-x)^(4*n))/(1+x^2) dx < 1/(2^(2*n-2) * (8*n+1) * binomial(8*n, 4*n)). So b(n) = 4 * Sum_{k=0..3*n-1} (-1)^k/(2*k+1) + (-1)^(n+1) * Sum_{k=0..2*n-1} (-1)^k/(2^(2*n-k-2) * (8*n-k-1) * binomial(8*n-k-2, 4*n+k)) is nearly Pi. And the limit of b(n) is Pi. LINKS Seiichi Manyama, Table of n, a(n) for n = 1..249 Jean-Christophe Pain, Successive approximations of Pi using Euler Beta functions, arXiv:2204.10693 [math.HO], 2022. See Table 1 p. 3. Wikipedia, Proof that 22/7 exceeds Pi EXAMPLE 1/1260 < 1/2^0 * Integral_{x=0..1} (x^4 * (1-x)^4)/(1+x^2) dx < 1/630. So 1/1260 < 22/7 - Pi < 1/630. 1/1750320 < 1/2^2 * Integral_{x=0..1} (x^8 * (1-x)^8)/(1+x^2) dx < 1/875160. So 1/1750320 < Pi - 47171/15015 < 1/875160. CROSSREFS Cf. A000796, A280813 (denominators). Sequence in context: A191946 A221639 A078398 * A060619 A238635 A013770 Adjacent sequences:  A280809 A280810 A280811 * A280813 A280814 A280815 KEYWORD nonn,frac AUTHOR Seiichi Manyama, Jan 08 2017 STATUS approved

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Last modified August 13 14:01 EDT 2022. Contains 356091 sequences. (Running on oeis4.)