17171...17171 (31-digits)

This number is a prime.

                                          1 7171717171 7171717171 7171717171

The smallest prime of the form 1(71)_k . [Adam]

The smallest smoothly undulating palindromic prime (SUPP) formed from digits 1 and 7. Curiously, the sum of its digits is the smallest smoothly undulating palindromic composite. [Silva]