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.

1, 13, 127, 1229, 12203, 122029, 1220203, 12202429, 122024299, 1220202089, 12202020043, 122020200859, 1220202000307, 12202020002059, 122020200020309, 1220202000202069, 12202020002020867, 122020200020200639

Offset

1,2

Comments

If n is composite then the least significant digit is mandatorily a 9. Conjecture: No term is zero.

Links

Table of n, a(n) for n=1..18.

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