Heptagonal numbers (Arith.), the numbers of the series 1, 7, 18, 34, 55, etc., being figurate numbers formed by adding successively the terms of the arithmetical series 1, 6, 11, 16, 21, etc.
... chapters of the pillars, on the inward front, a cupola was raised to cover the fountain. It was surrounded by the planetary statues, heptagonal at the bottom, and spherical o' top, and of crystal so pure, transparent, well-polished, whole and uniform in all its parts, without veins, clouds, flaws, or streaks, that Xenocrates never saw such ... — Gargantua and Pantagruel, Complete. • Francois Rabelais
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