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A025267
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a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ...+ a(n-1)*a(1) for n >= 4.
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0
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1, -1, 1, 3, 4, 3, 4, 19, 60, 124, 214, 455, 1266, 3404, 7974, 17699, 42050, 107956, 276534, 680140, 1647872, 4082562, 10366604, 26363583, 66318590, 166265630, 420151570, 1070885100, 2734066540, 6964626146, 17739885228, 45334834067, 116258144838
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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REFERENCES
| A. Cayley, On the Porism of the In-and-circumscribed Polygon, Collected Mathematical Papers. Vols. 1-13, Cambridge Univ. Press, London, 1889-1897, Vol. 4, 292-308 (see p. 300).
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FORMULA
| G.f.: (1-sqrt(1-4*x+8*x^2-12*x^3))/2.
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PROG
| (PARI) a(n)=polcoeff((1-sqrt(1-4*x+8*x^2-12*x^3+x*O(x^n)))/2, n)
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CROSSREFS
| Sequence in context: A006984 A087275 A072942 * A201420 A090739 A076400
Adjacent sequences: A025264 A025265 A025266 * A025268 A025269 A025270
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KEYWORD
| sign
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AUTHOR
| Clark Kimberling (ck6(AT)evansville.edu)
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EXTENSIONS
| Additional comments from Michael Somos, Apr 19, 2000
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