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A158768
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a(n)=39*(39*n^2+1).
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1
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39, 1560, 6123, 13728, 24375, 38064, 54795, 74568, 97383, 123240, 152139, 184080, 219063, 257088, 298155, 342264, 389415, 439608, 492843, 549120, 608439, 670800, 736203, 804648, 876135, 950664, 1028235, 1108848, 1192503, 1279200, 1368939
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| The identity (78*n^2+1)^2 - (1521*n^2+39) * (2*n)^2 = 1 can be written as
the Pell equation (A158769(n))^2 - a(n) * (A005843(n))^2 = 1.
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LINKS
| Wolfram MathWorld, Pell Equation
Edward Everett Withford, Pell Equation
Vincenzo Librandi, X^2-AY^2=1
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FORMULA
| a(n)= 3*a(n-1) -3*a(n-2) +a(n-3). G.f.: -39*(1+37*x+40*x^2)/(x-1)^3.
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CROSSREFS
| Cf. A005843, A158769
Sequence in context: A170758 A112617 A009983 * A139191 A176073 A145619
Adjacent sequences: A158765 A158766 A158767 * A158769 A158770 A158771
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KEYWORD
| nonn,easy
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AUTHOR
| Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Mar 26 2009
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EXTENSIONS
| Comment rewritten, a(0) added, and formula replaced by R. J. Mathar, (mathar(AT)strw.leidenuniv.nl), Oct 22 2009
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