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 A242299 Smallest composite number ending in 1, 3, 7, or 9 with n digits whose first n-1 digits are a(n-1). 0
 9, 91, 913, 9131, 91311, 913111, 9131111, 91311111, 913111111, 9131111111, 91311111111, 913111111113, 9131111111131, 91311111111311, 913111111113111, 9131111111131111, 91311111111311111, 913111111113111111, 9131111111131111111, 91311111111311111111 (list; graph; refs; listen; history; text; internal format)
 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 EXAMPLE 911 doesn't qualify for 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: A217959 A014992 A015585 * 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

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Last modified October 15 07:56 EDT 2019. Contains 328026 sequences. (Running on oeis4.)