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 A257745 Prime numbers that have a hexagonal Voronoi cell in the Voronoi diagram of the Ulam prime spiral. 1
 5, 7, 41, 43, 89, 127, 179, 193, 233, 263, 283, 317, 379, 383, 397, 443, 457, 487, 503, 547, 599, 607, 631, 643, 647, 719, 733, 787, 809, 821, 839, 937, 947, 971, 977, 997, 1019, 1039, 1049, 1069, 1091, 1097, 1103, 1109, 1187, 1193, 1217, 1231 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..48. Vardan Semerjyan, Voronoi diagram of prime spiral PROG (MATLAB) sz = 201; % Size of the N x N square matrix mat = spiral(sz); % MATLAB Function k = 1; for i =1:sz for j=1:sz if isprime(mat(i, j)) % Check if the number is prime % saving indices of primes y(k) = i; x(k) = j; k = k+1; end end end xy = [x', y']; [v, c] = voronoin(xy); % Returns Voronoi vertices V and % the Voronoi cells C k = 1; for i = 1:length(c) szv = size(v(c{i}, 1)); polyN(i) = szv(1); if polyN(i) == 6 A(k) = mat(y(i), x(i)); k = k+1; end end % Print terms A = sort(A); fprintf('A = '); fprintf('%i, ', A); % When running the code be aware that the last terms you get might not be correct. % They correspond to the points on the outer edges of the spiral which might be % altered when considering a larger spiral. % Use larger spiral to get more terms CROSSREFS Cf. A257527, A257528, A000040. Sequence in context: A154148 A340818 A242241 * A153376 A235139 A263448 Adjacent sequences: A257742 A257743 A257744 * A257746 A257747 A257748 KEYWORD nonn AUTHOR Vardan Semerjyan, May 07 2015 STATUS approved

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Last modified December 2 09:50 EST 2023. Contains 367517 sequences. (Running on oeis4.)