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Search: id:A071119
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| A071119 |
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Palindromic primes in which deleting the outside pair of digits yields a prime at every stage until finally a single-digit prime is obtained. |
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+0
3
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| 2, 3, 5, 7, 131, 151, 353, 373, 727, 757, 929, 11311, 31513, 33533, 37273, 37573, 39293, 71317, 93739, 97579, 1335331, 3315133, 3392933, 7392937, 9375739, 373929373, 733929337
(list; graph; listen)
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OFFSET
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1,1
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REFERENCES
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J.-P. Delahaye, "Pour la science", (French edition of Scientific American), Juin 2002, p. 99.
G. L. Honaker, Jr. and C. Caldwell, Palindromic prime pyramids, J. Recreational Mathematics, vol. 30.3, pp. 169-176, 1999-2000.
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LINKS
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G. L. Honaker, Jr. and C. K. Caldwell, Palindromic Prime Pyramids
G. L. Honaker, Jr. and C. K. Caldwell, Supplement to "Palindromic Prime Pyramids"
I. Peterson, MathTrek, Primes, Palindromes and Pyramids
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EXAMPLE
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31513 is in the sequence because 31513, 151 and 5 are primes.
a(17) = 39293 because 39293, 929 and 2 are primes.
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PROGRAM
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(PARI) V = [2, 3, 5, 7]; vCount = 4; x = [1, 3, 7, 9]; print(V); forstep (i = 2, 20, 2, newV = vector(4*vCount); newCount = 0; for (j = 1, 4, for (k = 1, vCount, n = x[j]*(10^i + 1) + 10*V[k]; if (isprime(n), print(n); newCount = newCount + 1; newV[newCount] = n))); V = newV; vCount = newCount) - David Wasserman (wasserma(AT)spawar.navy.mil), Oct 04 2004
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CROSSREFS
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Cf. A002385.
Sequence in context: A039944 A076611 A082805 this_sequence A157869 A046705 A054218
Adjacent sequences: A071116 A071117 A071118 this_sequence A071120 A071121 A071122
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KEYWORD
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base,easy,fini,full,nonn
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AUTHOR
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Lior Manor (lior.manor(AT)gmail.com) May 28 2002
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EXTENSIONS
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Edited by N. J. A. Sloane (njas(AT)research.att.com) at the suggestion of Andrew Plewe, May 14 2007
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