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A226638
Product of Pell and Lucas numbers.
2
0, 1, 6, 20, 84, 319, 1260, 4901, 19176, 74860, 292494, 1142459, 4462920, 17433181, 68099226, 266014100, 1039126224, 4059116419, 15856045380, 61938144041, 241947712356, 945115407340, 3691885043874, 14421535219799, 56334548849040, 220058498917081
OFFSET
0,3
FORMULA
Recurrence: a(n) = 2a(n-1) + 7a(n-2) + 2a(n-3) - a(n-4), n>3, starting 0,1,6,20.
G.f.: x*(x^2 + 4*x + 1)/(x^4 - 2*x^3 - 7*x^2 - 2*x + 1).
a(n) = A000129(n) * A000032(n).
MATHEMATICA
LinearRecurrence[{2, 7, 2, -1}, {0, 1, 6, 20}, 30] (* Harvey P. Dale, Sep 26 2016 *)
PROG
(PARI) pell(n)=if(n<2, n>0, 2*pell(n-1)+pell(n-2))
lucas(n)=if(n<1, 2*(n>=0), fibonacci(n-1)+fibonacci(n+1))
a(n)=pell(n)*lucas(n)
(PARI) concat([0], Vec(x*(x^2+4*x+1)/(x^4-2*x^3-7*x^2-2*x+1)+O(x^66))) \\ Joerg Arndt, Sep 01 2013
CROSSREFS
Sequence in context: A118265 A204271 A255469 * A274071 A246036 A151485
KEYWORD
nonn,easy
AUTHOR
Ralf Stephan, Sep 01 2013
STATUS
approved