

A084413


Smallest prime with "n" as central digit(s), or 1 if no such prime exists.


4



101, 113, 2, 3, 149, 5, 163, 7, 181, 191, 1103, 11, 1123, 13, 2141, 1151, 1163, 17, 1181, 19, 1201, 1213, 1223, 23, 1249, 1259, 2267, 1277, 1283, 29, 1301, 31, 1321, 2333, 2341, 2351, 1361, 37, 1381, 1399, 1409, 41, 1423, 43, 1447, 1451, 2467, 47, 1481
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OFFSET

0,1


COMMENTS

For n=5620 and n=7358, adding only one digit to both sides do not result in any prime.  Robert Price, Sep 16 2023


LINKS



FORMULA



EXAMPLE

a(1)=113 because 113 is the smallest prime with "1" as central digit.
a(10)=1103 because 1103 is the smallest prime with "10" as central digits.


PROG

(PARI) findex(n) = {for (i = 1, 9, forstep (j=1, 9, 2, v = j + 10*n + i*10^(1+length(Str(n))); if (isprime(v), return (v)); ); ); }
a(n) = if (isprime(n), n, findex(n)); \\ code assumes only 1 digit on each side of 'n' will be necessary. See A032734 for numbers that need a better script.  Michel Marcus, Oct 05 2013


CROSSREFS



KEYWORD

easy,nonn,base,changed


AUTHOR



EXTENSIONS



STATUS

approved



