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A105609
Sylvester numbers for 1/(1+x^2).
3
1, 0, -1, -2, 1, -3, -1, 2, -1, 5, -1, 1, 1, -7, 1, 2, 1, -3, -1, 1, 1, -11, -1, 1, 1, 13, -1, 1, 1, 1, -1, 2, 1, 17, 1, 1, 1, -19, 1, 1, 1, 1, -1, 1, 1, -23, -1, 1, -1, 5, 1, 1, 1, -3, 1, 1, 1, 29, -1, 1, 1, -31, 1, 2, 1, 1, -1, 1, 1, 1, -1, 1, 1, 37
OFFSET
0,4
LINKS
Peter Luschny and Stefan Wehmeier, The lcm(1,2,...,n) as a product of sine values sampled over the points in Farey sequences, arXiv:0909.1838 [math.CA], 2009.
Eric Weisstein's World of Mathematics, Sylvester Cyclotomic Number.
FORMULA
a(n) = Product_{k=1..n} if(gcd(n+1, k)=1, (I+I*exp(2*Pi*I*k/(n+1))), 1), I=sqrt(-1).
alpha(n) = Product_{0<k<n} if(gcd(k,n)=1, 2*cos(Pi*k/n), 1); a(n) = alpha(n+1). Cf. the formula in A014963 with cos replaced by sin. - Peter Luschny, Jun 09 2011
EXAMPLE
(x+I)(x-I)=1+x^2
MAPLE
A105609 := proc(n)local k: round(Re(mul(evalf(`if`(gcd(n+1, k)=1, I+I*exp(2*Pi*I*k/(n+1)), 1)), k=1..n))): end:
seq(A105609(n), n=0..20); # Nathaniel Johnston, Apr 20 2011
A105609 := proc(n) local k; mul(`if`(igcd(n+1, k)=1, 2*cos(Pi*k/(n+1)), 1), k=1..n) end; seq(round(A105609(n)), n = 0..73); # Peter Luschny, Jun 09 2011
MATHEMATICA
f[n_] := FullSimplify[ Expand[Times @@ (I + I*Exp[2Pi*I*Select[Range[n], GCD[ #, n] == 1 &]/n])]]; Table[ f[n], {n, 0, 32}] (* Robert G. Wilson v, Aug 02 2005 *)
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, Apr 15 2005
EXTENSIONS
a(40)-a(73) from Nathaniel Johnston, Apr 20 2011
STATUS
approved