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440, 881, 1322, 1763, 2204, 2645, 3086, 3527, 3968, 4409, 4850, 5291, 5732, 6173, 6614, 7055, 7496, 7937, 8378, 8819, 9260, 9701, 10142, 10583, 11024, 11465, 11906, 12347, 12788, 13229, 13670, 14111, 14552, 14993, 15434, 15875, 16316, 16757
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| The identity (441*n-1)^2-(441*n^2-2*n)*(21)^2=1 can be written as a(n)^2-A157737(n)*(21)^2=1.
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 1..10000
Vincenzo Librandi, X^2-AY^2=1
E. J. Barbeau, Polynomial Excursions, Chapter 10: Diophantine equations (2010), pages 84-85 (row 15 in the first table at p. 85, case d(t) = t*(21^2*t-2)).
Index to sequences with linear recurrences with constant coefficients, signature (2,-1).
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FORMULA
| a(n) = 2*a(n-1)-a(n-2).
G.f.: x*(440+x)/(1-x)^2.
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MATHEMATICA
| LinearRecurrence[{2, -1}, {440, 881}, 50]
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PROG
| (MAGMA) I:=[440, 881]; [n le 2 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..50]];
(PARI) a(n) = 441*n - 1.
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CROSSREFS
| Cf. A157737.
Sequence in context: A192857 A092048 A072604 * A061626 A187239 A124170
Adjacent sequences: A158316 A158317 A158318 * A158320 A158321 A158322
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KEYWORD
| nonn,easy
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AUTHOR
| Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Mar 16 2009
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