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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.
0
3, 4, 7, 13, 25, 34, 37, 97
OFFSET
1,1
COMMENTS
First unknown: 361.
EXAMPLE
a(4) = 13 so 1234567891234 = 2 * 617283945617 is a semiprime.
CROSSREFS
Cf. A057137.
Sequence in context: A280224 A282718 A092406 * A254310 A121174 A050071
KEYWORD
nonn,base
AUTHOR
Eric Chen, Dec 26 2014
STATUS
approved