16723...99999 (200-digits)

This number is a prime.

           1672375728 3622817643 9702951352 2593146688 1865832845 0745257391
7838075408 3893112407 4734171854 1317996245 3270394094 7330352263 8133602147
3520304649 7462027859 7412501491 2401303142 3999999999 9999999999 9999999999

+ Frank Morgan's "Math Chat" column (1997) challenged readers to find the largest prime number by using four 4's and a finite number of mathematical symbols and operators in common use. William Foster had the best submission: ((sqrt(4)/.4)!! - .4)/.4. [Brahinsky]

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