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A157667
a(n) = 531441*n^2 - 740664*n + 258065.
3
48842, 902501, 2819042, 5798465, 9840770, 14945957, 21114026, 28344977, 36638810, 45995525, 56415122, 67897601, 80442962, 94051205, 108722330, 124456337, 141253226, 159112997, 178035650, 198021185, 219069602, 241180901
OFFSET
1,1
COMMENTS
The identity (531441*n^2 - 740664*n + 258065)^2 - (729*n^2 - 1016*n + 354)*(19683*n - 13716)^2 = 1 can be written as a(n)^2 - A157665(n)*A157666(n)^2 = 1.
FORMULA
a(n) = 3*a(n-1) - 3*a(n-2) +a (n-3).
G.f.: x*(48842 + 755975*x + 258065*x^2)/(1-x)^3.
E.g.f.: (258065 - 209223*x + 531441*x^2)*exp(x) - 258065. - G. C. Greubel, Nov 17 2018
MATHEMATICA
LinearRecurrence[{3, -3, 1}, {48842, 902501, 2819042}, 40]
PROG
(Magma) I:=[48842, 902501, 2819042]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]];
(PARI) a(n) = 531441*n^2 - 740664*n + 258065.
(Sage) [531441*n^2 - 740664*n + 258065 for n in (1..40)] # G. C. Greubel, Nov 17 2018
(GAP) List([1..40], n -> 531441*n^2 - 740664*n + 258065); # G. C. Greubel, Nov 17 2018
CROSSREFS
Sequence in context: A067869 A175278 A336189 * A176373 A237087 A061737
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Mar 04 2009
STATUS
approved