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Search: id:A158739
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| 36, 1332, 5220, 11700, 20772, 32436, 46692, 63540, 82980, 105012, 129636, 156852, 186660, 219060, 254052, 291636, 331812, 374580, 419940, 467892, 518436, 571572, 627300, 685620, 746532, 810036, 876132, 944820, 1016100, 1089972, 1166436
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OFFSET
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0,1
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COMMENT
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The identity (72*n^2+1)^2 - (1296*n^2+36) * (2*n)^2 = 1 can be written as
the Pell equation (A158740(n))^2 - a(n) * (A005843(n))^2 = 1.
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LINKS
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Wolfram MathWorld, Pell Equation
Vincenzo Librandi, X^2-AY^2=1
Edward Everett Withford, Pell Equation
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FORMULA
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a(n)= 3*a(n-1) -3*a(n-2) +a(n-3). G.f.: -36*(1+34*x+37*x^2)/(x-1)^3.
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CROSSREFS
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Cf. A005843, A158740
Sequence in context: A144128 A009980 A041613 this_sequence A099366 A095657 A034996
Adjacent sequences: A158736 A158737 A158738 this_sequence A158740 A158741 A158742
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KEYWORD
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nonn,easy
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AUTHOR
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Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Mar 25 2009
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EXTENSIONS
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Comment rewritten, a(0) added and formula replaced by R. J. Mathar, (mathar(AT)strw.leidenuniv.nl), Oct 22 2009
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