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 A089763 a(1) = 1, then the least n-digit prime such that the k-th digit from the Most significant side is prime if k is prime else is composite. The most significant digit is always a 1. 0 if no such prime exists. 0
 1, 13, 127, 1229, 12203, 122029, 1220203, 12202429, 122024299, 1220202089, 12202020043, 122020200859, 1220202000307, 12202020002059, 122020200020309, 1220202000202069, 12202020002020867, 122020200020200639 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS If n is composite then the least significant digit is mandatorily a 9. Conjecture: No term is zero. LINKS EXAMPLE a(8) = 12202429: first digit is 1, the 2nd, 3rd, 5th and 7th digits are 2 (a prime) and the rest are composite. MAPLE with(combinat, cartprod): ds:=proc(s) local j, l: l:=nops(s): RETURN(add(s[j]*10^(l-j), j=1..l)):end: p:=[2, 3, 5, 7]:c:=[0, 4, 8, 6, 9]: ctpr:=proc(n) local m, T: m:=1: T:=cartprod([[1], seq(piecewise(isprime(i), p, c), i=2..n)]): while not T[finished] do m:=ds(T[nextvalue]()): if isprime(m) then RETURN(m) fi od: end: 1, seq(ctpr(n), n=1..20); (C. Ronaldo) CROSSREFS Sequence in context: A139786 A016169 A125401 * A124298 A201040 A201550 Adjacent sequences:  A089760 A089761 A089762 * A089764 A089765 A089766 KEYWORD base,nonn AUTHOR Amarnath Murthy, Nov 22 2003 EXTENSIONS More terms from C. Ronaldo (aga_new_ac(AT)hotmail.com), Dec 26 2004 STATUS approved

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Last modified October 13 20:38 EDT 2019. Contains 327981 sequences. (Running on oeis4.)