A255605 Integer part of the area of a pentagon with side length n.
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
Offset: 1
Keywords
Links
- Harvey P. Dale, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
Table[IntegerPart[5*n^2/(4*Tan[Pi/5])], {n, 51}] (* Michael De Vlieger, Mar 18 2015 *) With[{c=Sqrt[25+10*Sqrt[5]]/4},Table[IntegerPart[c*n^2],{n,60}]] (* Harvey P. Dale, Aug 17 2020 *) -
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
Formula
a(n) = floor(5*n^2/(4*tan(Pi/5))), n >= 1.
Comments