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

1,1

Comments

First unknown: 361.

Links

Table of n, a(n) for n=1..8.

Example

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

Crossrefs

Cf. A057137.

Sequence in context: A280224 A282718 A092406 * A254310 A121174 A050071

Adjacent sequences: A250294 A250295 A250296 * A250298 A250299 A250300

Keyword

nonn,base

Author

Eric Chen, Dec 26 2014

Status

approved