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Divergent Infinite Geometric Series

An infinite geometric series is divergent when the absolute value of its common ratio satisfies r1|r| \geq 1. In a divergent series, each term is at least as large as the one before it (or does not shrink toward zero), so the partial sums keep growing without bound as more terms are added. Because the partial sums never settle down to a single number, no finite sum exists for a divergent infinite geometric series.

For example, the series 3+6+12+24+48+96+3 + 6 + 12 + 24 + 48 + 96 + \dots has a1=3a_1 = 3 and r=2r = 2. Since r=21|r| = 2 \geq 1, the series is divergent. Computing a few partial sums confirms this: S10=3,069S_{10} = 3{,}069, S30=3,221,225,469S_{30} = 3{,}221{,}225{,}469, and S503.38imes1015S_{50} \approx 3.38 imes 10^{15}. Each partial sum is vastly larger than the previous one, showing that the total grows without limit.

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Updated 2026-05-25

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