noun: an integer that has no integral factors but itself and 1

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In the figure,

See Also

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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 SpiralSee 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****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**