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Search: id:A076611
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| A076611 |
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Palindromic primes with prime middle digit. |
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+0
2
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| 2, 3, 5, 7, 131, 151, 353, 373, 727, 757, 929, 10301, 10501, 11311, 12721, 13331, 14341, 14741, 15551, 16361, 16561, 19391, 30203, 30703, 31513, 32323, 33533, 34543, 35353, 35753, 36263, 36563, 37273, 37573, 38783, 39293, 70207, 70507
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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There are no such numbers with an even number of digits. This sequence is quite similar to the sequence A071119 up to 12th term.
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EXAMPLE
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a(12)=10301 is palindromic prime and its middle digit 3 is prime, a(13)=10501 is palindromic prime and its middle digit 5 is prime, a(14)=11311 is palindromic prime and its middle digit 3 is prime, ...
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MAPLE
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ts_numprapal := proc(n) local ad, adr, midigit; ad := convert(n, base, 10): adr := ListTools[Reverse](ad): if nops(ad) mod 2 = 0 then return 1; fi; midigit := op( (nops(ad)+1)/2, ad ): if (isprime( midigit )='true' and adr=ad) then return 0; else return 1; fi end: ts_pra_num_pal := proc(n) local p1; p1 := ithprime(n): if ts_numprapal(p1) = 0 then return (p1) fi end: apranumpal := [seq(ts_pra_num_pal(i), i=1..100000)]: apranumpal;
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CROSSREFS
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Cf. A002385, A069217, A071119.
Adjacent sequences: A076608 A076609 A076610 this_sequence A076612 A076613 A076614
Sequence in context: A090718 A117703 A039944 this_sequence A082805 A071119 A157869
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KEYWORD
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easy,nonn,base
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AUTHOR
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Jani Melik (jani_melik(AT)hotmail.com), Oct 21 2002
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