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Search: id:A137812
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| A137812 |
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Left- or right-truncatable primes. |
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+0
1
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| 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
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Repeatedly removing a digit from either the left or right produces only primes. There are 149677 terms in this sequence, ending with 8939662423123592347173339993799.
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REFERENCES
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Angell, I. O. and Godwin, H. J. "On Truncatable Primes." Math. Comput. 31, 265-267, 1977.
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..10000
Index entries for sequences related to truncatable primes
Carlos Rivera, Puzzle 2: Prime Strings
Eric Weisstein, MathWorld: Truncatable Prime
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EXAMPLE
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139 is here because (removing 9 from the right) 13 is prime and (removing 1 from the left) 3 is prime.
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MATHEMATICA
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Clear[s]; s[0]={2, 3, 5, 7}; n=1; While[s[n]={}; Do[k=s[n-1][[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[n-1]]}]; s[n]=Union[s[n]]; Length[s[n]]>0, n++ ]; t=s[0]; Do[t=Join[t, s[i]], {i, n}]; t
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CROSSREFS
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Cf. A024770, A024785, A080608.
Sequence in context: A090422 A005109 A080608 this_sequence A094317 A074834 A089438
Adjacent sequences: A137809 A137810 A137811 this_sequence A137813 A137814 A137815
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KEYWORD
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base,nonn
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AUTHOR
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T. D. Noe (noe(AT)sspectra.com), Feb 11 2008
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