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A255605 Integer part of the area of a pentagon with side length n. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 3 of A255604.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = floor(5*n^2/(4*tan(Pi/5))), n >= 1.

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 *)

PROG

(PARI){for(n=1, 100, a=floor(5*n^2/(4*tan(Pi/5))); print1(a, ", "))}

CROSSREFS

Cf. A102771, A255604.

Sequence in context: A227952 A316320 A140091 * A171972 A225285 A165454

Adjacent sequences:  A255602 A255603 A255604 * A255606 A255607 A255608

KEYWORD

nonn

AUTHOR

Kival Ngaokrajang, Feb 27 2015

STATUS

approved

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Last modified September 26 12:00 EDT 2020. Contains 337371 sequences. (Running on oeis4.)