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20, 95, 220, 395, 620, 895, 1220, 1595, 2020, 2495, 3020, 3595, 4220, 4895, 5620, 6395, 7220, 8095, 9020, 9995, 11020, 12095, 13220, 14395, 15620, 16895, 18220, 19595, 21020, 22495, 24020, 25595, 27220, 28895, 30620, 32395, 34220, 36095
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| The identity (10*n^2-1)^2-(25*n^2-5)*(2*n)^2=1 can be written as A158447(n)^2-a(n)*A005843(n)^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
Index to sequences with linear recurrences with constant coefficients, signature (3,-3,1).
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FORMULA
| a(n) = 3*a(n-1) -3*a(n-2) +a(n-3).
G.f: 5*x*(4+7*x-x^2)/(1-x)^3.
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MATHEMATICA
| Table[25n^2-5, {n, 50}]
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PROG
| (MAGMA) I:=[20, 95, 220]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+Self(n-3): n in [1..50]];
(PARI) a(n) = 25*n^2 - 5.
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CROSSREFS
| Cf. A005843, A158447.
Sequence in context: A144359 A124948 A126407 * A039610 A177498 A157429
Adjacent sequences: A158443 A158444 A158445 * A158447 A158448 A158449
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KEYWORD
| nonn,easy
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AUTHOR
| Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Mar 19 2009
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