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A118005 a(n) = ((-1)^n*5^(n+1) + 9^(n+1))/14. 1
1, 4, 61, 424, 4441, 36844, 347221, 3046864, 27812401, 248358484, 2244991981, 20156099704, 181649037961, 1633620638524, 14708689262341, 132347685782944, 1191281759937121, 10720772899980964, 96490770797094301 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
COMMENTS
Number of black cells after n iterations of Haferman's carpet.
LINKS
Eric Weisstein's World of Mathematics, Haferman Carpet
FORMULA
From Colin Barker, Jun 08 2013: (Start)
a(n) = 4*a(n-1) + 45*a(n-2).
G.f.: -1 / ((5*x+1)*(9*x-1)).
(End)
PROG
(PARI) Vec(1 / ((1 + 5*x)*(1 - 9*x)) + O(x^40)) \\ Colin Barker, Feb 26 2020
CROSSREFS
Sequence in context: A158300 A129452 A131014 * A132064 A229666 A252973
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Apr 09 2006
STATUS
approved

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Last modified March 29 10:59 EDT 2024. Contains 371277 sequences. (Running on oeis4.)