

A060919


Number of corners in a 4sided fractal.


6



4, 8, 20, 60, 204, 748, 2860, 11180, 44204, 175788, 701100, 2800300, 11193004, 44755628, 178989740, 715893420, 2863442604, 11453508268, 45813508780, 183252986540, 733009849004, 2932035201708, 11728132418220, 46912512895660
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OFFSET

1,1


LINKS

Harry J. Smith, Table of n, a(n) for n=1,...,200
H. Bottomley, Illustration of initial terms
Index entries for linear recurrences with constant coefficients, signature (7,14,8).


FORMULA

a(n) =4^n/6+2^n+4/3 =(2^n+2)*(2^n+4)/6 =4*A007581(n1) =4(a(n1)1)2^n =A028400(n1)A002450(n1)
a(n) = 7*a(n1)14*a(n2)+8*a(n3). G.f.: 4*x*(5*x^25*x+1) / ((x1)*(2*x1)*(4*x1)). [Colin Barker, Nov 28 2012]


PROG

(PARI) { for (n=1, 200, write("b060919.txt", n, " ", (2^n + 2)*(2^n + 4)/6); ) } \\ Harry J. Smith, Jul 14 2009


CROSSREFS

Sequence in context: A203167 A123861 A115099 * A009333 A187010 A240149
Adjacent sequences: A060916 A060917 A060918 * A060920 A060921 A060922


KEYWORD

nonn,easy


AUTHOR

Henry Bottomley, Apr 10 2001


STATUS

approved



