

A232129


Largest prime that can be obtained from n by successively appending digits to the right with the constraint that each of the numbers obtained that way must be prime; a(n)=0 if there is no such prime at all.


3



1979339339, 29399999, 37337999, 4391339, 59393339, 6733997, 73939133, 839, 9719, 103997939939, 113, 12791333, 13999133, 149399, 15797, 1637, 17333, 1811993, 1979339339, 0, 21139, 2273993, 23399339, 24179399, 2579939, 2699393, 27191939, 2837, 29399999, 3079, 31379, 0, 331999799, 3491333, 35393999
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OFFSET

1,1


COMMENTS

See A232128 for the number of steps required to reach a(n), equal to the length of a(n) minus the length of n. See A232126 for a variant "working backwards", where truncation is considered.


LINKS

Table of n, a(n) for n=1..35.
Archimedes' Lab, What's Special About This Number?, section about 43.


EXAMPLE

Starting with 8, one can get the primes 83 and 89 which is larger, but 83 allows one further extension to 839 while 89 does not (no prime in the range 890..899. No further extension is possible, since there are no primes in the range 8390,...,8399. Therefore a(8)=839 and A232128(8)=2.
a(20)=a(42)=0 since no prime can be obtained by appending one digit to 20 or 42.


PROG

(PARI) {A232129(n)=local(t(p)=my(m, r=[0, p]); forstep(d=1, 9, 2, isprime(p*10+d)&&(m=t(10*p+d)+[1, 0])[1]>=r[1]&&r=m); r); n<(n=t(n))[2]&&return(n[2])}


CROSSREFS

Cf. A232128, A232127, A232126, A232125.
Sequence in context: A017363 A017483 A017615 * A251506 A259349 A204416
Adjacent sequences: A232126 A232127 A232128 * A232130 A232131 A232132


KEYWORD

nonn,base


AUTHOR

M. F. Hasler, Nov 19 2013


STATUS

approved



