A242299 a(n) is the smallest composite number ending in 1, 3, 7, or 9 with n digits whose first n-1 digits are a(n-1).

9, 91, 913, 9131, 91311, 913111, 9131111, 91311111, 913111111, 9131111111, 91311111111, 913111111113, 9131111111131, 91311111111311, 913111111113111, 9131111111131111, 91311111111311111, 913111111113111111, 9131111111131111111, 91311111111311111111

Offset

1,1

Comments

Question: do only a finite number of terms end in a digit other than 1?

Question: is the sequence infinite?

Links

Table of n, a(n) for n=1..20.

Example

911 is not a(3) because 911 is prime.

Prog

(PARI) lista(nn) = {vi = [1, 3, 7, 9]; a = 9; print1(a, ", "); for (n=1, nn, ok = 0; for (i=1, #vi, if (!isprime(na = eval(concat(Str(a), Str(vi[i])))), ok = 1; break; ); ); if (!ok, print("end of sequence"); return(); ); a = na; print1(a, ", "); ); } \\ Michel Marcus, May 11 2014

Crossrefs

Sequence in context: A014992 A015585 A366393 * A109108 A163456 A318593

Adjacent sequences: A242296 A242297 A242298 * A242300 A242301 A242302

Keyword

nonn,base

Author

J. Lowell, May 10 2014

Extensions

More terms from Michel Marcus, May 11 2014

Status

approved