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A255605
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Integer part of the area of a pentagon with side length n.
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3
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1, 6, 15, 27, 43, 61, 84, 110, 139, 172, 208, 247, 290, 337, 387, 440, 497, 557, 621, 688, 758, 832, 910, 990, 1075, 1163, 1254, 1348, 1446, 1548, 1653, 1761, 1873, 1988, 2107, 2229, 2355, 2484, 2616, 2752, 2892, 3034, 3181, 3330, 3483, 3640, 3800, 3963, 4130, 4301, 4474
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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a(n) = floor(5*n^2/(4*tan(Pi/5))), n >= 1.
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MATHEMATICA
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With[{c=Sqrt[25+10*Sqrt[5]]/4}, Table[IntegerPart[c*n^2], {n, 60}]] (* Harvey P. Dale, Aug 17 2020 *)
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PROG
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(PARI){for(n=1, 100, a=floor(5*n^2/(4*tan(Pi/5))); print1(a, ", "))}
(PARI) my(c=25+10*quadgen(20)); a(n) = sqrtint(floor(c*n^4))>>2; \\ Kevin Ryde, May 07 2021
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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