A084414 - OEIS

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A084414

Smallest prime > n having "n" as central digits(s), or -1 if no such prime exists.

101, 113, 127, 131, 149, 151, 163, 173, 181, 191, 1103, 1117, 1123, 2131, 2141, 1151, 1163, 1171, 1181, 1193, 1201, 1213, 1223, 1231, 1249, 1259, 2267, 1277, 1283, 1291, 1301, 1319, 1321, 2333, 2341, 2351, 1361, 1373, 1381, 1399, 1409, 2411, 1423, 1433, 1447

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,1

COMMENTS

a(n) >= A084413(n), with equality when n is prime. - Michel Marcus, Oct 05 2013

For n=2437, 5620 and 7358 adding one digit on each side of n does not produce any prime. - Robert Price, Sep 16 2023

LINKS

Robert Price, Table of n, a(n) for n = 0..2000

Index entries for primes involving decimal expansion of n

EXAMPLE

a(1)=113 because 113 is the smallest prime >1 having "1" as central digit.

PROG

(PARI) a(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)); ); ); } \\ 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

Cf. A030665, A069691, A077501, A084413.

Sequence in context: A084413 A248533 A069691 * A164937 A105992 A038370

Adjacent sequences: A084411 A084412 A084413 * A084415 A084416 A084417

KEYWORD

easy,nonn,base

AUTHOR

Zak Seidov, Jun 24 2003

EXTENSIONS

a(21) inserted and more terms from Michel Marcus, Oct 05 2013

Escape clause added by N. J. A. Sloane, Nov 11 2020

STATUS

approved