A216453 Number of points hidden from the central point by a closer point in a hexagonal orchard of order n.

0, 6, 12, 24, 30, 54, 60, 84, 102, 138, 144, 192, 198, 246, 288, 336, 342, 414, 420, 492, 546, 618, 624, 720, 750, 834, 888, 984, 990, 1122, 1128, 1224, 1302, 1410, 1476, 1620, 1626, 1746, 1836, 1980, 1986, 2166, 2172, 2316, 2442, 2586, 2592, 2784, 2826, 3006, 3120, 3288, 3294, 3510, 3600, 3792, 3918

Offset

1,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..5000

Project Euler, Problem 351: Hexagonal orchards.

Formula

a(n) = 6 * (C(n+1,2) - Sum_{i=1..n} phi(i)). - corrected by Piyush Kumar and Robert Israel, Aug 26 2014

a(n) = 6*A063985(n). - Jon Maiga, Jan 12 2019

Mathematica

Table[6*Sum[k - EulerPhi[k], {k, n}], {n, 100}] (* Jon Maiga, Jan 12 2019 *)

Prog

(PARI) for(i=1, 100, print1(6*(binomial(i+1, 2)-sum(X=1, i, eulerphi(X))), ", "))

Crossrefs

Cf. A063985.

Sequence in context: A358526 A069171 A071611 * A119500 A260633 A348632

Adjacent sequences: A216450 A216451 A216452 * A216454 A216455 A216456

Keyword

nonn

Author

V. Raman, Sep 07 2012

Status

approved