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 A164985 Denominators of ternary BBP-type series for log(5) 3
 1, 6, 27, 405, 1458, 5103, 59049, 196830, 649539, 6908733, 22320522, 71744535, 731794257, 2324522934, 7360989291, 73222472421, 230127770466, 721764371007, 7060738412025, 22029503845518, 68630377364883, 663426981193869 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The formula log(5)=(4/27)Sum(k>=0,(1/81^k)(9/(4k+1)+3/(4k+2)+1/(4k+3))) can be written in unit numerators: log(5)=(4/3)Sum(k>=0,(1/81^k)(1/(4k+1)+1/(3*(4k+2))+1/(9*(4k+3)))), so the sequence of denominators inside the sum satisfies Sum(n>=0,1/a(n))=(3/4)log(5) LINKS FORMULA G.f.: (1+6*x+27*x^2+243*x^3+486*x^4+729*x^5)/(1-81*x^3)^2 PROG (PARI) a(n)=[(n\3*4+1), 3*(n\3*4+2), 9*(n\3*4+3)][n%3+1]*81^(n\3) CROSSREFS Cf. A154920. Sequence in context: A047778 A290802 A322233 * A048436 A276412 A006174 Adjacent sequences:  A164982 A164983 A164984 * A164986 A164987 A164988 KEYWORD frac,nonn AUTHOR Jaume Oliver Lafont, Sep 03 2009 STATUS approved

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Last modified October 21 06:18 EDT 2019. Contains 328292 sequences. (Running on oeis4.)