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 A065520 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. 1
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 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 LINKS EXAMPLE 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. PROG (Perl) for(\$n=1; \$n<=999; \$n++){   print "\$i, " if(\$n =~ /^[123579][1379]*\$/) } # Charles R Greathouse IV, Jan 02 2013 (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 CROSSREFS Cf. A004022, A004023. Sequence in context: A305078 A328336 A305103 * A316428 A277702 A279516 Adjacent sequences:  A065517 A065518 A065519 * A065521 A065522 A065523 KEYWORD base,nonn,easy AUTHOR Friedrich Laher (fritzl7(AT)netscape.net), Nov 27 2001 EXTENSIONS Corrected and extended by Frank Ellermann, Dec 10 2001 Corrected by T. D. Noe, Nov 01 2006 a(31) from Charles R Greathouse IV, Jan 02 2013 STATUS approved

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Last modified January 19 20:41 EST 2020. Contains 331066 sequences. (Running on oeis4.)