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 A257746 Prime numbers that have a heptagonal (7 sides) Voronoi cell in the Voronoi diagram of the Ulam prime spiral. 0
 61, 157, 199, 311, 349, 409, 463, 509, 557, 601, 641, 691, 727, 757, 823, 911, 919, 1051, 1093, 1123, 1153, 1213, 1327, 1433, 1459, 1627, 1951, 2027, 2063, 2221, 2251, 2293, 2311, 2357, 2389, 2551, 2621, 2683, 2719, 2789, 2791, 2939, 2953 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..43. Vardan Semerjyan, Voronoi diagram of prime spiral PROG (MATLAB) clc clear all 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) == 7 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: A211333 A252811 A252804 * A062661 A044393 A044774 Adjacent sequences: A257743 A257744 A257745 * A257747 A257748 A257749 KEYWORD nonn AUTHOR Vardan Semerjyan, May 07 2015 STATUS approved

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Last modified December 10 04:38 EST 2023. Contains 367699 sequences. (Running on oeis4.)