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Search: id:A101782
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| A101782 |
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Upper bound of twin prime pairs whose digital reverse is prime. |
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+0
1
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| 5, 7, 13, 31, 73, 151, 181, 199, 313, 1021, 1033, 1153, 1231, 1279, 1321, 1429, 1453, 1669, 1723, 1789, 1879, 1933, 3121, 3169, 3301, 3373, 3391, 3463, 3469, 3541, 3583, 3853, 7459, 7561, 7879, 7951, 9001, 9013, 9241, 9421, 9439, 9679, 9721, 9769, 9931
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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13 is the upper bound of twin prime pair (11,13) and its digital reverse, 31, is prime.
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PROGRAM
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(PARI) twurpr(n) = { for(x=1, n, y=twinu(x); z=eval(rev(y)); if(isprime(z), print1(y", ")) ) } twinu(n) = \The n-th upper twin prime { local(c, x); c=0; x=1; while(c<n, if(isprime(prime(x)+2), c++); x++; ); return(prime(x)) } rev(str) = \ Get the reverse of the input string { local(tmp, s, j); tmp = Vec(Str(str)); s=""; forstep(j=length(tmp), 1, -1, s=concat(s, tmp[j])); return(s) }
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CROSSREFS
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Sequence in context: A124307 A090610 A141191 this_sequence A018464 A063446 A064600
Adjacent sequences: A101779 A101780 A101781 this_sequence A101783 A101784 A101785
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KEYWORD
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easy,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Jan 26 2005
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