| The (double) Primorial sieve & Prime spirals |
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The counterclockwise Ulam spiral (1963) with startvalue 0 is defined by eight families of functions. With these families of functions ANY area of the spiral can be examined, without building the spiral from the ground up (see above).
Excel can be used to further examine the Ulam spiral using just the four functions of the North, East, South and West sector. The Excel sheet contains examples of how to use these functions, even with different startvalues.
These same principles (based on a Cartesian coordinate system) can be used in any (large) computer program.
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