13

This number is a prime.

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The smallest prime that when concatenated to its Collatz sequence (13 --> 40 --> 20 --> 10 --> 5 --> 16 --> 8 --> 4-2-1) inexorable ending 4-2-1 forms another prime: 13421. Note that a reverse concatenation also yields a prime (12413). [Beedassy]

Submitted: 2009-11-07 11:31:45;   Last Modified: 2014-08-30 15:16:45.
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