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 A089704 Primes in which the unit place digit is 1 and the k-th most significant digit is prime (2,3,5,7) if k is prime else is composite (4,6,8,9,0). 2
 31, 71, 251, 271, 331, 521, 571, 751, 4231, 4271, 4721, 4751, 6221, 6271, 6521, 6551, 6571, 8221, 8231, 8521, 8731, 9221, 9371, 9521, 9551, 9721, 20231, 20521, 20551, 20731, 20771, 24251, 24371, 24551, 24571, 26251, 26321, 26371, 26731, 28351 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS EXAMPLE 6271 is a member as unit place digit is 1, second MSD is prime, third MSD is prime and the fourth MSD is 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, 6, 8, 9]: ctpr:=proc(n, s) local m, T, a: a:=s: m:=1: T:=cartprod([seq(piecewise(isprime(n-i+2), p, c), i=2..n), [1]]): while not T[finished] do m:=ds(T[nextvalue]()): if isprime(m) and not member(m, a) then a:=[op(a), m] fi od: RETURN(a): end: a:=[]: for n from 1 to 5 do a:=ctpr(n, a) od: op(a); # C. Ronaldo CROSSREFS Cf. A089705. Sequence in context: A050957 A127345 A127346 * A287609 A210548 A146353 Adjacent sequences:  A089701 A089702 A089703 * A089705 A089706 A089707 KEYWORD base,nonn AUTHOR Amarnath Murthy, Nov 10 2003 EXTENSIONS More terms from C. Ronaldo (aga_new_ac(AT)hotmail.com), Dec 25 2004 STATUS approved

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Last modified May 26 18:04 EDT 2019. Contains 323597 sequences. (Running on oeis4.)