19

This number is a prime.

The first prime repfigit number. A repfigit (repetitive fibonacci-like digit) number is an n-digit integer N with the following property: if a Fibonacci-like sequence (in which each term in the sequence is the sum of the n previous terms) is formed, with the first n terms being the decimal digits of the number N, then N itself occurs as a term in the sequence. For example, if the digits of 19 start a Fibonacci-like sequence, then 19 appears as a term: 1, 9, 10, 19. These are also known as Keith numbers. [Beedassy]