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A257746 Prime numbers that have a heptagonal (7 sides) Voronoi cell in the Voronoi diagram of the Ulam prime spiral.

%I A257746 #7 Dec 16 2017 18:01:59
%S A257746 61,157,199,311,349,409,463,509,557,601,641,691,727,757,823,911,919,
%T A257746 1051,1093,1123,1153,1213,1327,1433,1459,1627,1951,2027,2063,2221,
%U A257746 2251,2293,2311,2357,2389,2551,2621,2683,2719,2789,2791,2939,2953
%N A257746 Prime numbers that have a heptagonal (7 sides) Voronoi cell in the Voronoi diagram of the Ulam prime spiral.
%H A257746 Vardan Semerjyan, <a href="http://smallsats.org/2014/01/03/voronoi-diagram-of-prime-spiral/">Voronoi diagram of prime spiral</a>
%o A257746 (MATLAB)
%o A257746 clc
%o A257746 clear all
%o A257746 sz  = 201; % Size of the N x N square matrix
%o A257746 mat = spiral(sz); % MATLAB Function
%o A257746 k = 1;
%o A257746 for i =1:sz
%o A257746     for j=1:sz
%o A257746         if isprime(mat(i,j)) % Check if the number is prime
%o A257746             % saving indices of primes
%o A257746             y(k) = i; x(k) = j;
%o A257746             k = k+1;
%o A257746         end
%o A257746     end
%o A257746 end
%o A257746 xy = [x',y'];
%o A257746 [v,c] = voronoin(xy); %  Returns Voronoi vertices V and
%o A257746 % the Voronoi cells C
%o A257746 k = 1;
%o A257746 for i = 1:length(c)
%o A257746   szv = size(v(c{i},1));
%o A257746   polyN(i) = szv(1);
%o A257746   if polyN(i) == 7
%o A257746         A(k) = mat(y(i),x(i));
%o A257746         k = k+1;
%o A257746       end
%o A257746 end
%o A257746 % Print terms
%o A257746 A = sort(A);
%o A257746 fprintf('A = ');
%o A257746 fprintf('%i, ',A);
%o A257746 % When running the code be aware that the last terms you get might not be correct.
%o A257746 % They correspond to the points on the outer edges of the spiral which might be
%o A257746 % altered when considering a larger spiral.
%o A257746 % Use larger spiral to get more terms
%Y A257746 Cf. A257527, A257528, A000040.
%K A257746 nonn
%O A257746 1,1
%A A257746 _Vardan Semerjyan_, May 07 2015