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A032437
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Substrings from the right are prime numbers (using only odd digits different from 5).
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12
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3, 7, 13, 17, 37, 73, 97, 113, 137, 173, 197, 313, 317, 337, 373, 397, 773, 797, 937, 997, 1373, 1997, 3137, 3313, 3373, 3797, 7937, 9137, 9173, 9337, 9397, 13313, 33797, 39397, 79337, 79397, 91373, 91997, 99137, 99173, 99397, 139397, 379397
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OFFSET
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1,1
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COMMENTS
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Primes p with decimal expansion d_1 d_2 d_3 ... d_k such that the digits d_i are 1, 3, 7, or 9, and deleting 1, 2, 3, up to k-1 leading digits also produces a prime. For example, 9173 is a term because all of 9173, 173, 73, and 3 are primes. - N. J. A. Sloane, Jun 28 2022
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LINKS
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EXAMPLE
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173 is a term because 173, 73, and 3 are all primes. 371 is not a term because 371 and 1 are not primes. - N. J. A. Sloane, Jun 28 2022
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MATHEMATICA
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Select[Prime[Range[33000]], SubsetQ[{1, 3, 7, 9}, IntegerDigits[#]]&&AllTrue[Mod[#, 10^Range[ IntegerLength[ #]-1]], PrimeQ]&] (* Harvey P. Dale, Jun 28 2022 *)
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PROG
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(PARI) is(n)=my(d=digits(n)); for(i=1, n, if(!isprime(fromdigits(d[i..n])), return(0))); 1 \\ Charles R Greathouse IV, Jun 25 2017
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CROSSREFS
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KEYWORD
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nonn,fini,full,base,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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