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Search: id:A076612
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| A076612 |
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Palindromic numbers with nonprime middle digit. |
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+0
1
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| 1, 4, 6, 8, 9, 101, 111, 141, 161, 181, 191, 202, 212, 242, 262, 282, 292, 303, 313, 343, 363, 383, 393, 404, 414, 444, 464, 484, 494, 505, 515, 545, 565, 585, 595, 606, 616, 646, 666, 686, 696, 707, 717, 747, 767, 787, 797, 808, 818, 848, 868, 888, 898, 909
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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a(12)=202=2*101 is palindromic number and its middle digit 0 is not prime, a(13)=212=2^2*53 is palindromic number and its middle digit 1 is not prime, a(14)=242=2*11^2 is palindromic number and its middle digit 4 is not prime, ...
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MAPLE
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ts_num_midpal := 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 )='false' and adr=ad) then return 0; else return 1; fi end: ts_n_pal := proc(n) if ts_num_midpal(n) = 0 then return (i) fi end: anpal := [seq(ts_n_pal(i), i=1..50000)]: anpal;
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CROSSREFS
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Cf. A002113.
Sequence in context: A113624 A113591 A029581 this_sequence A046354 A046357 A144123
Adjacent sequences: A076609 A076610 A076611 this_sequence A076613 A076614 A076615
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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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