A250297 Number n such that the n-th term of "concatenate next digit at right hand end (where the next digit after 9 is again 1)" is a semiprime.

3, 4, 7, 13, 25, 34, 37, 97

Offset: 1

Author

Eric Chen, Dec 26 2014

Keywords

• nonn
• base

Comments

First unknown: 361.

Examples

			a(4) = 13 so 1234567891234 = 2 * 617283945617 is a semiprime.
		

Crossrefs

Cf. A057137.