23161

This number is a composite.

The concatenation in order of first three pentanacci primes, (2, 31, 61), is a 2-sphenic number, i.e., 23161 = 19 x 23 x 53. Cutting the largest prime and putting it in front of the concatenation of the other two, 231, we create 61231, that is the only prime formed from the above pentanacci primes. [Loungrides]