A pyramidal number is a figurate number that represents a pyramid with a base and a given number of sides. The term is most often used to refer to square pyramidal numbers, which have four sides, but it can also refer to:
- Triangular pyramidal number (three sides)
- Square pyramidal number (four sides)
- Pentagonal pyramidal number (five sides)
- Hexagonal pyramidal number (six sides)
- Heptagonal pyramidal number (seven sides)
The formula for a r-gonal pyramid number is:
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“... in every State there are more women who can read and write than the whole number of illiterate male voters; more white women who can read and write than all Negro voters; more American women who can read and write than all foreign voters.”
—National Woman Suffrage Association. As quoted in History of Woman Suffrage, vol. 4, ch. 13, by Susan B. Anthony and Ida Husted Harper (1902)
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