Search: id:A137812
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%I A137812
%S A137812 2,3,5,7,13,17,23,29,31,37,43,47,53,59,67,71,73,79,83,97,113,131,137,
%T A137812 139,167,173,179,197,223,229,233,239,271,283,293,311,313,317,331,337,
%U A137812 347,353,359,367,373,379,383,397,431,433,439,443,467,479,523,547,571
%N A137812 Left- or right-truncatable primes.
%C A137812 Repeatedly removing a digit from either the left or right produces only 
               primes. There are 149677 terms in this sequence, ending with 8939662423123592347173339993799.
%D A137812 Angell, I. O. and Godwin, H. J. "On Truncatable Primes." Math. Comput. 
               31, 265-267, 1977.
%H A137812 T. D. Noe, <a href="b137812.txt">Table of n, a(n) for n=1..10000</a>
%H A137812 <a href="Sindx_Tri.html#tprime">Index entries for sequences related to 
               truncatable primes</a>
%H A137812 Carlos Rivera, <a href="http://www.primepuzzles.net/puzzles/puzz_002.htm">
               Puzzle 2: Prime Strings</a>
%H A137812 Eric Weisstein, <a href="http://mathworld.wolfram.com/TruncatablePrime.html">
               MathWorld: Truncatable Prime</a>
%e A137812 139 is here because (removing 9 from the right) 13 is prime and (removing 
               1 from the left) 3 is prime.
%t A137812 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
%Y A137812 Cf. A024770, A024785, A080608.
%Y A137812 Sequence in context: A090422 A005109 A080608 this_sequence A094317 A074834 
               A089438
%Y A137812 Adjacent sequences: A137809 A137810 A137811 this_sequence A137813 A137814 
               A137815
%K A137812 base,nonn
%O A137812 1,1
%A A137812 T. D. Noe (noe(AT)sspectra.com), Feb 11 2008

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