noun: an integer that has no integral factors but itself and 1.
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Ulam's Spiral
In the figure, primes appear to concentrate along certain diagonal lines. In the 200×200 Ulam spiral shown above, diagonal lines are clearly visible, confirming that the pattern continues. Horizontal and vertical lines with a high density of primes, while less prominent, are also evident. Most often, the number spiral is started with the number 1 at the center, but it is possible to start with any number, and the same concentration of primes along diagonal, horizontal, and vertical lines is observed. Starting with 41 at the center gives a particularly impressive example, with a diagonal containing an unbroken string of 40 primes, part of which is shown below. Wikipedia, Ulam's Spiral
See Also
Indig Numbers
Number
prime
prime conductors
Prime Fraction Equivalent
Prime Neutral Center
Prime Third
Sympsionics Numbers
Table 11.03 - Roots Powers of Two and Indig Numbers
Ulam Spiral
11.12 - Hidden Powers of Numbers
11.14 - Indig Numbers
11.15 - Indig Numbers - Inert Gases and Octave Position
11.16 - Indig Numbers and the Power of the Powers of Two
12.21 - Fibonacci Whole Numbers v Irrational Decimal near Equivalents