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A320519
a(n) = 2*n^n*cos(n*arcsin(sqrt(4*n^2-1)/(2*n))) for n > 0 and a(0) = 2.
2
2, 1, -7, -26, 449, 3001, -81863, -790271, 29441537, 371653678, -17549650999, -273657699479, 15647990550337, 290477695697281, -19502273553366631, -419946226750915874, 32375641678132277249, 793304922112119056161, -69057016330377072921047, -1897210272812469982747199
OFFSET
0,1
FORMULA
For n > 0, a(n) = n^n*(h(n)^(-n) + h(n)^n) where h(n) = (1 + i*sqrt(4*n^2 - 1))/(2*n).
For n > 0, a(n) = 2 * n^n * cos(n*arctan(sqrt(4*n^2 - 1))). - Vladimir Reshetnikov, Oct 14 2018
CROSSREFS
Cf. A320534.
Sequence in context: A141516 A235378 A214327 * A183272 A138346 A085073
KEYWORD
sign
AUTHOR
Peter Luschny, Oct 14 2018
STATUS
approved