71

This number is a prime.

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Place the emirps in order of 71,73,79 to get 17+37+79 = 133 = 7*19 with sum of digits 7+1+9 = 17, which is the first number in 17+37+73. Add 71+73+79=223 with sum of digits 2+2+3=7, the first digit of all 71,73,79. [Bergot]

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