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 A220448 Define a sequence u(n) by u(1)=1; thereafter u(n) = f(n)/f(n-1) where f(n) = (-1)^(n+1)*A105750(n); sequence gives numerator(u(n)). 3
 1, 1, -10, -1, 19, -73, 662, -2795, 281, -4511, 21746, -322921, 1035215, -720817, 1077518, -87995911, -34376687, 929280875, -92673902, 6986985769, -33833494045, 243540693677, -1817775985570, 13097400661955, -27199287430171, 8249498995171439, -112427012362483262, 3008079144099400625, -10365435567354511181 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Also u(n) = n*x(n-1)-1, where x(n) is defined in A220447. LINKS V. H. Moll, An arithmetic conjecture on a sequence of arctangent sums, 2012. EXAMPLE The sequence u(n) begins 1, 1, -10, -1, 19, -73/19, 662/73, -2795/331, 281/43, -4511/281, 21746/4511, ... MAPLE A220448 := proc(n)     if n= 1 then         1 ;     else         -A105750(n)/A105750(n-1) ;         numer(%) ;     end if; end proc: # R. J. Mathar, Jan 04 2013 CROSSREFS Denominator(u(n)) = A220447(n-1). Sequence in context: A209924 A209926 A016530 * A059920 A040109 A317054 Adjacent sequences:  A220445 A220446 A220447 * A220449 A220450 A220451 KEYWORD sign,frac AUTHOR N. J. A. Sloane, Dec 22 2012 STATUS approved

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Last modified October 15 03:04 EDT 2019. Contains 328025 sequences. (Running on oeis4.)