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A151980
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Numbers n such that n^2 - n is divisible by 20.
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3
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0, 1, 5, 16, 20, 21, 25, 36, 40, 41, 45, 56, 60, 61, 65, 76, 80, 81, 85, 96, 100, 101, 105, 116, 120, 121, 125, 136, 140, 141, 145, 156, 160, 161, 165, 176, 180, 181, 185, 196, 200, 201, 205, 216, 220, 221, 225, 236, 240, 241, 245, 256, 260, 261, 265, 276, 280, 281, 285, 296
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OFFSET
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1,3
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LINKS
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FORMULA
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G.f.: x^2*(1+4*x+11*x^2+4*x^3)/((1-x)^2*(1+x)*(1+x^2)). [Colin Barker, Jan 14 2012]
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MATHEMATICA
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Select[Range[0, 300], Divisible[#^2-#, 20]&] (* or *) LinearRecurrence[ {1, 0, 0, 1, -1}, {0, 1, 5, 16, 20}, 60] (* Harvey P. Dale, Aug 16 2020 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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