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A065520
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Numbers n with the property that if m is formed from n by dropping any number (possibly zero) of initial or final digits then there is a prime ending with m.
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1
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1, 2, 3, 5, 7, 9, 11, 13, 17, 19, 21, 23, 27, 29, 31, 33, 37, 39, 51, 53, 57, 59, 71, 73, 77, 79, 91, 93, 97, 99, 111, 113, 117, 119, 131, 133, 137, 139, 171, 173, 177, 179, 191, 193, 197, 199, 211, 213, 217, 219, 231, 233, 237, 239, 271, 273, 277, 279, 291, 293, 297
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OFFSET
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1,2
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COMMENTS
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Are all the numbers represented by the regular expressions ([2|5])[1|3|7|9]+ in this sequence?
Yes. In fact the members of this sequence are just those represented by the regular expression [123579][1379]* and hence the sequence is 10-automatic. - Charles R Greathouse IV, Jan 02 2013
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LINKS
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EXAMPLE
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199 is in the sequence since there are primes that end with 199, 19, 99, 1 and 9 (namely 199, 19, 199, 11 and 19). 41 is not in the sequence since no primes ends with 4.
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PROG
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(Perl) for($n=1; $n<=999; $n++){
print "$i, " if($n =~ /^[123579][1379]*$/)
(PARI) is(n)=my(d=digits(n)); (d[1]%2 || d[1]==2) && (#d<2 || vecsort(concat([1, 3, 7, 9], d[2..#d]), , 8)==[1, 3, 7, 9]) \\ Charles R Greathouse IV, Jan 02 2013
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CROSSREFS
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KEYWORD
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base,nonn,easy
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AUTHOR
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Friedrich Laher (fritzl7(AT)netscape.net), Nov 27 2001
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EXTENSIONS
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STATUS
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approved
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