

A137812


Left or righttruncatable primes.


7



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.


REFERENCES

Angell, I. O. and Godwin, H. J. "On Truncatable Primes." Math. Comput. 31, 265267, 1977.


LINKS

T. D. Noe, Table of n, a(n) for n=1..10000
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: A234851 A179336 A080608 * A216578 A094317 A074834
Adjacent sequences: A137809 A137810 A137811 * A137813 A137814 A137815


KEYWORD

base,fini,nonn


AUTHOR

T. D. Noe, Feb 11 2008


STATUS

approved



