

A232125


Smallest prime such that the n numbers obtained by removing 1 digit on the right are also prime, while no digit can be added on the right to get another prime.


5



53, 53, 317, 2393, 23333, 373393, 2399333, 23399339, 1979339333, 103997939939, 4099339193933, 145701173999399393
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OFFSET

0,1


COMMENTS

Inspired by article on 43 in Archimedes' Lab link.


LINKS

Table of n, a(n) for n=0..11.
G. A. Sarcone and M. J. Waeber, What's Special About This Number?, Archimedes' Lab website.


EXAMPLE

a(0)=53 because 53 is the smallest prime such that all numbers obtained by adding a digit to the right are composite.
a(1)=53 because 5 and 53 are primes.
a(2)=317 because 3, 31, 317 are all primes, and 317 has the same property as 53 when adding a digit to the right.


PROG

(PARI) a(n) = {n++; v = vector(n); i = 1; ok = 0; until (ok, while ((i>1) && (v[i] == 9), v[i] = 0; i); if (i == 1, v[i] = nextprime(v[i]+1), v[i] = v[i]+1); curp = sum (j=1, i, v[j]*(10^(ij))); if (isprime(curp), if (i != n, i++, nbp = 0; for (z=1, 9, if (isprime(10*curp+z), nbp++); ); if (nbp == 0, ok = 1); ); ); ); sum (j=1, n, v[j]*(10^(nj))); }


CROSSREFS

Sequence in context: A109648 A109733 A094462 * A343794 A042403 A217609
Adjacent sequences: A232122 A232123 A232124 * A232126 A232127 A232128


KEYWORD

nonn,base,more


AUTHOR

Michel Marcus, Nov 19 2013


STATUS

approved



