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The least composite odd number that is the sum of the primes between its smallest and largest prime factors (39 = 3 * 13 = 3 + 5 + 7 + 11 + 13). [Rivera] Concatenating the 39th row numbers of Pascal's triangle forms a prime. [Rivera] 39 is the smallest positive integer which cannot be formed from the first four primes (used once each), using only the simple operations +, , *, / and ^. [Hartley] 39 = 3*9 + (39) [Firoozbakht] (39) = 3 + 9. [Gupta] 39 = nextprime(3+9)*((3+9)). The two numbers 39 and reversal(nextprime(39)) are the only numbers with this property. [Hasler] The number formed by concatenating the nonprime integers 1 through 39 is the smallest such prime: 1468910121415161820212224252627283032333435363839. [Loungrides]
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