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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

%I

%S 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,

%T 79,91,93,97,99,111,113,117,119,131,133,137,139,171,173,177,179,191,

%U 193,197,199,211,213,217,219,231,233,237,239,271,273,277,279,291,293,297

%N 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.

%C Are all the numbers represented by the regular expressions ([2|5])[1|3|7|9]+ in this sequence?

%C 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

%H <a href="/index/Ar#10-automatic">Index entries for 10-automatic sequences</a>.

%e 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.

%o (Perl) for(\$n=1;\$n<=999;\$n++){

%o print "\$i, " if(\$n =~ /^[123579][1379]*\$/)

%o } # _Charles R Greathouse IV_, Jan 02 2013

%o (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

%Y Cf. A004022, A004023.

%K base,nonn,easy

%O 1,2

%A Friedrich Laher (fritzl7(AT)netscape.net), Nov 27 2001

%E Corrected and extended by _Frank Ellermann_, Dec 10 2001

%E Corrected by _T. D. Noe_, Nov 01 2006

%E a(31) from _Charles R Greathouse IV_, Jan 02 2013

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Last modified February 24 22:04 EST 2020. Contains 332216 sequences. (Running on oeis4.)