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 A128500 Numerators of partial sums for a series for Pi/(3*sqrt(3)). 2
 1, 1, 1, 3, 11, 11, 97, 159, 159, 187, 1777, 1777, 26181, 23321, 23321, 51647, 797919, 797919, 16521821, 15228529, 15228529, 16404249, 351431887, 351431887, 1876142299, 1761735699, 1761735699, 1867970399, 51196569971, 51196569971 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS The denominators are given in A128501. The limit n -> infinity of the rationals r(n) defined below is Pi/(3*sqrt(3). LINKS W. Lang, Rationals and limit. FORMULA a(n)=numerator(r(n)) with the rationals r(n):=sum(((-1)^k)*S(k,1)/(k+1),k=0..n) with Chebyshev's S-Polynomials S(k,1)=[1,1,0,-1,-1,0] periodic sequence with period 6. See A010892. EXAMPLE Rationals: [1, 1/2, 1/2, 3/4, 11/20, 11/20, 97/140, 159/280, 159/280, 187/280,...] Pi/(3*sqrt(3))=+1/1 -1/2 +1/4 -1/5 +1/7 -1/8 +1/10 -1/11 +1/13 -+ CROSSREFS Sequence in context: A059200 A232038 A072980 * A043051 A024545 A101134 Adjacent sequences:  A128497 A128498 A128499 * A128501 A128502 A128503 KEYWORD nonn,frac,easy AUTHOR Wolfdieter Lang Apr 04 2007 STATUS approved

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Last modified December 7 05:14 EST 2019. Contains 329839 sequences. (Running on oeis4.)