To picture 10^18, just picture 10^13, but then imagine you connect the left side of the 3 to close off the little bays.

"Exa-Exabyte", by Randall Munroe, licensed under Creative Commons Attribution-NonCommercial 2.5 License

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To picture 10^18, just picture 10^13, but then imagine you connect the left side of the 3 to close off the little bays.