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A145020
a(n) = ((7 + sqrt(7))^n - (7 - sqrt(7))^n)^2/28.
0
1, 196, 23716, 2458624, 239754256, 22776846400, 2139058352704, 199857257119744, 18630079167234304, 1734834007938712576, 161472109634377851904, 15026063825688651366400
OFFSET
1,2
FORMULA
From R. J. Mathar, Sep 30 2008: (Start)
G.f.: x(1+42x)/((1-42x)(1-112x+1764x^2)).
a(n) = 154*a(n-1) - 6468*a(n-2) + 74088*a(n-3). (End)
PROG
(Magma) Z<x>:=PolynomialRing(Integers()); N<r7>:=NumberField(x^2-7); [ Integers()!a: a in [ ((7+r7)^n-(7-r7)^n)^2/28: n in [1..12] ] ]; // Klaus Brockhaus, Oct 20 2008
CROSSREFS
Sequence in context: A035834 A114761 A076002 * A333641 A260863 A351683
KEYWORD
nonn,easy
AUTHOR
Al Hakanson (hawkuu(AT)gmail.com), Sep 29 2008
EXTENSIONS
Extended by R. J. Mathar, Sep 30 2008
STATUS
approved