

A020994


Primes that are both lefttruncatable and righttruncatable.


12



2, 3, 5, 7, 23, 37, 53, 73, 313, 317, 373, 797, 3137, 3797, 739397
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OFFSET

1,1


COMMENTS

Twosided primes: deleting any number of digits at left or at right, but not both, leaves a prime.
Primes in which every digit string containing the most significant digit or the least significant digit is prime.  Amarnath Murthy, Sep 24 2003


REFERENCES

Angell, I. O. and Godwin, H. J. "On Truncatable Primes." Math. Comput. 31, 265267, 1977.
David Wells, The Penguin Dictionary of Curious and Interesting Numbers, p. 178 (Rev. ed. 1997).


LINKS

Table of n, a(n) for n=1..15.
P. De Geest, The list of 4260 lefttruncatable primes
Index entries for sequences related to truncatable primes


MATHEMATICA

tspQ[n_] := Module[{idn=IntegerDigits[n], l}, l=Length[idn]; Union[PrimeQ/@(FromDigits/@ Join[Table[Take[idn, i], {i, l}], Table[Take[idn, i], {i, l}]])]=={True}] Select[Prime[Range[PrimePi[740000]]], tspQ]


CROSSREFS

Cf. A033664, A024785, A032437, A024770, A052023, A052024, A052025, A050986, A050987.
Sequence in context: A211681 A124674 A177061 * A085823 A211682 A100552
Adjacent sequences: A020991 A020992 A020993 * A020995 A020996 A020997


KEYWORD

nonn,fini,full,base


AUTHOR

Mario Velucchi (mathchess(AT)velucchi.it)


EXTENSIONS

Corrected by David W. Wilson.
Additional comments from Harvey P. Dale, Jul 10 2002


STATUS

approved



