

A137812


Left or righttruncatable primes.


8



2, 3, 5, 7, 13, 17, 23, 29, 31, 37, 43, 47, 53, 59, 67, 71, 73, 79, 83, 97, 113, 131, 137, 139, 167, 173, 179, 197, 223, 229, 233, 239, 271, 283, 293, 311, 313, 317, 331, 337, 347, 353, 359, 367, 373, 379, 383, 397, 431, 433, 439, 443, 467, 479, 523, 547, 571
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OFFSET

1,1


COMMENTS

Repeatedly removing a digit from either the left or right produces only primes. There are 149677 terms in this sequence, ending with 8939662423123592347173339993799.


LINKS

T. D. Noe, Table of n, a(n) for n=1..10000
I. O. Angell and H. J. Godwin, On Truncatable Primes, Math. Comput. 31, 265267, 1977.
T. D. Noe, Plot of all terms
Carlos Rivera, Puzzle 2: Prime Strings
Eric Weisstein, MathWorld: Truncatable Prime
Index entries for sequences related to truncatable primes


EXAMPLE

139 is here because (removing 9 from the right) 13 is prime and (removing 1 from the left) 3 is prime.


MATHEMATICA

Clear[s]; s[0]={2, 3, 5, 7}; n=1; While[s[n]={}; Do[k=s[n1][[i]]; Do[p=j*10^n+k; If[PrimeQ[p], AppendTo[s[n], p]], {j, 9}]; Do[p=10*k+j; If[PrimeQ[p], AppendTo[s[n], p]], {j, 9}], {i, Length[s[n1]]}]; s[n]=Union[s[n]]; Length[s[n]]>0, n++ ]; t=s[0]; Do[t=Join[t, s[i]], {i, n}]; t


CROSSREFS

Cf. A024770 (righttruncatable primes), A024785 (lefttruncatable primes), A077390 (leftandright truncatable primes), A080608.
Sequence in context: A080608 A305352 A322473 * A216578 A094317 A074834
Adjacent sequences: A137809 A137810 A137811 * A137813 A137814 A137815


KEYWORD

base,fini,nonn


AUTHOR

T. D. Noe, Feb 11 2008


STATUS

approved



