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Search: id:A076609
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| A076609 |
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Palindromic numbers with prime middle digit. |
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+0
1
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| 2, 3, 5, 7, 121, 131, 151, 171, 222, 232, 252, 272, 323, 333, 353, 373, 424, 434, 454, 474, 525, 535, 555, 575, 626, 636, 656, 676, 727, 737, 757, 777, 828, 838, 858, 878, 929, 939, 959, 979, 10201, 10301, 10501, 10701, 11211, 11311, 11511, 11711, 12221
(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 with an even number of digits.
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EXAMPLE
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a(12)=272=2^4*17 is palindromic number and its middle digit 7 is prime, a(13)=323=17*19 is palindromic number and its middle digit 2 is prime, a(14)=333=3^2*37 is palindromic number 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_num_pal := proc(i) if ts_numprapal(i) = 0 then return (i) fi end: anumpal := [seq(ts_num_pal(i), i=1..50000)]: anumpal;
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CROSSREFS
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Cf. A032350.
Adjacent sequences: A076606 A076607 A076608 this_sequence A076610 A076611 A076612
Sequence in context: A086107 A046713 A119835 this_sequence A117059 A117058 A067173
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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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