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A164080
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Perfect squares one less than a triangular number.
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2
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0, 9, 324, 11025, 374544, 12723489, 432224100, 14682895929, 498786237504, 16944049179225, 575598885856164, 19553418069930369, 664240615491776400, 22564627508650467249, 766533094678624110084, 26039560591564569275625
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = 35*a(n-1) -35*a(n-2) +a(n-3) = 9*A001110(n-1). G.f.: 9*x^2*(1+x)/((1-x)*(x^2-34*x+1)). [R. J. Mathar, Oct 21 2009]
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EXAMPLE
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324=18^2 is a perfect square and 325=A000217(25) is a triangular number. Therefore 324 is in this sequence.
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MATHEMATICA
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LinearRecurrence[{35, -35, 1}, {0, 9, 324}, 20] (* Harvey P. Dale, Oct 24 2023 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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