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A060919 Number of corners in a 4-sided 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 (list; graph; refs; listen; history; text; internal format)
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(n-1) =4(a(n-1)-1)-2^n =A028400(n-1)-A002450(n-1)

a(n) = 7*a(n-1)-14*a(n-2)+8*a(n-3). G.f.: -4*x*(5*x^2-5*x+1) / ((x-1)*(2*x-1)*(4*x-1)). [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

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Last modified December 12 23:01 EST 2018. Contains 318081 sequences. (Running on oeis4.)