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 A002264 Nonnegative integers repeated 3 times. 113
 0, 0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5, 6, 6, 6, 7, 7, 7, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 11, 12, 12, 12, 13, 13, 13, 14, 14, 14, 15, 15, 15, 16, 16, 16, 17, 17, 17, 18, 18, 18, 19, 19, 19, 20, 20, 20, 21, 21, 21, 22, 22, 22, 23, 23, 23, 24, 24, 24, 25 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,7 COMMENTS Complement of A010872, since A010872(n) + 3*a(n) = n. - Hieronymus Fischer, Jun 01 2007 Chvátal proved that, given an arbitrary n-gon, there exist a(n) points such that all points in the interior are visible from at least one of those points; further, for all n >= 3, there exists an n-gon which cannot be covered in this fashion with fewer than a(n) points. This is known as the "art gallery problem". - Charles R Greathouse IV, Aug 29 2012 LINKS Michael De Vlieger, Table of n, a(n) for n = 0..10000 Václav Chvátal, A combinatorial theorem in plane geometry, Journal of Combinatorial Theory, Series B 18 (1975), pp. 39-41, doi:10.1016/0095-8956(75)90061-1. Clark Kimberling, A Combinatorial Classification of Triangle Centers on the Line at Infinity, J. Int. Seq., Vol. 22 (2019), Article 19.5.4. Index entries for linear recurrences with constant coefficients, signature (1,0,1,-1). FORMULA a(n) = floor(n/3). a(n) = -1 + Sum_{k=0..n} (-2*(k mod 3) + ((k+1) mod 3) + 4*((k+2) mod 3))/9. - Paolo P. Lava, Jun 20 2007 a(n) = (3*n-3-sqrt(3)*(1-2*cos(2*Pi*(n-1)/3))*sin(2*Pi*(n-1)/3)))/9. - Hieronymus Fischer, Sep 18 2007 a(n) = (n - A010872(n))/3. - Hieronymus Fischer, Sep 18 2007 Complex representation: a(n) = (n - (1 - r^n)*(1 + r^n/(1 - r)))/3 where r = exp(2*Pi/3*i) = (-1 + sqrt(3)*i)/2 and i = sqrt(-1). - Hieronymus Fischer, Sep 18 2007; - corrected by Guenther Schrack, Sep 26 2019 a(n) = Sum_{k=0..n-1} A022003(k). - Hieronymus Fischer, Sep 18 2007 G.f.: x^3/((1-x)*(1-x^3)). - Hieronymus Fischer, Sep 18 2007 a(n) = (n - 1 + 2*sin(4*(n+2)*Pi/3)/sqrt(3))/3. - Jaume Oliver Lafont, Dec 05 2008 For n >= 3, a(n) = floor(log_3(3^a(n-1) + 3^a(n-2) + 3^a(n-3))). - Vladimir Shevelev, Jun 22 2010 a(n) = (n - 3 + A010872(n-1) + A010872(n-2))/3 using Zumkeller's 2008 formula in A010872. - Adriano Caroli, Nov 23 2010 a(n) = A004526(n) - A008615(n). - Reinhard Zumkeller, Apr 28 2014 a(2*n) = A004523(n) and a(2*n+1) = A004396(n). - L. Edson Jeffery, Jul 30 2014 a(n) = n - 2 - a(n-1) - a(n-2) for n > 1 with a(0) = a(1) = 0. - Derek Orr, Apr 28 2015 From Wesley Ivan Hurt, May 27 2015: (Start) a(n) = a(n-1) + a(n-3) - a(n-4), n > 4. a(n) = (n - 1 + 0^((-1)^(n/3) - (-1)^n) - 0^((-1)^(n/3)*(-1)^(1/3) + (-1)^n))/3. (End) a(n) = (3*n - 3 + r^n*(1 - r) + r^(2*n)*(r + 2))/9 where r = (-1 + sqrt(-3))/2. - Guenther Schrack, Sep 26 2019 E.g.f.: exp(x)*(x - 1)/3 + exp(-x/2)*(3*cos(sqrt(3)*x/2) + sqrt(3)*sin(sqrt(3)*x/2))/9. - Stefano Spezia, Oct 17 2022 MAPLE P:=proc(n) local a, i, k; for i from 0 by 1 to n do a:=-1+sum('1/9*(-2*(k mod 3)+((k+1) mod 3)+4*((k+2) mod 3))', 'k'=0..i); print(a); od; end: P(100); # Paolo P. Lava, Jun 20 2007 # Alternative: seq(i\$3, i=0..100); # Robert Israel, Aug 04 2014 MATHEMATICA Flatten[Table[{n, n, n}, {n, 0, 25}]] (* Harvey P. Dale, Jun 09 2013 *) PROG (PARI) a(n)=n\3 /* Jaume Oliver Lafont, Mar 25 2009 */ (Sage) [floor(n/3) for n in range(0, 79)] # Zerinvary Lajos, Dec 01 2009 (Haskell) a002264 n = a002264_list !! n a002264_list = 0 : 0 : 0 : map (+ 1) a002264_list -- Reinhard Zumkeller, Nov 06 2012, Apr 16 2012 (PARI) v=[0, 0]; for(n=2, 50, v=concat(v, n-2-v[#v]-v[#v-1])); v \\ Derek Orr, Apr 28 2015 (Magma) [Floor(n/3): n in [0..100]]; // Vincenzo Librandi, Apr 29 2015 (Magma) &cat [[n, n, n]: n in [0..30]]; // Bruno Berselli, Apr 29 2015 CROSSREFS Cf. A001477, A002265, A002266, A004526, A008615, A008620, A010761, A010762, A010872, A010873, A010874, A022003, A110532, A110533. Partial sums give A130518. Cf. A004523 interlaced with A004396. Apart from the zeros, this is column 3 of A235791. Sequence in context: A261231 A296357 A086161 * A008620 A104581 A261916 Adjacent sequences: A002261 A002262 A002263 * A002265 A002266 A002267 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified December 5 18:02 EST 2022. Contains 358588 sequences. (Running on oeis4.)