Sexsexagintasescentillion is the 666th illion in googology, a very large number, equal to 10²⁰⁰¹, i.e.,
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To put it into perspective, there are an estimated total of 10⁸⁰ quantum particles in the known universe, and thus there are not enough quantum particles in the known universe to count to 1 Sexsexagintasescentillion, making the known universe short by 10¹⁹²¹ quantum particles. In other words, the size of the known universe is hardly anything compared to the size of 1 Sexsexagintasescentillion.