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Search: id:A076613
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| A076613 |
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Palindromic primes with nonprime middle digit. |
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+0
1
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| 101, 181, 191, 313, 383, 787, 797, 919, 10601, 11411, 12421, 12821, 13831, 13931, 15451, 16061, 16661, 17471, 17971, 18181, 18481, 19891, 19991, 30103, 30403, 30803, 31013, 32423, 34843, 35053, 35153, 38083, 38183, 70607, 71917, 73037
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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a(12)=12821 is palindromic prime and its middle digit 8 is not prime, a(13)=13831 is palindromic prime and its middle digit 8 is not prime, a(14)=13931 is palindromic prime and its middle digit 9 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_pra_n_pal := proc(n) local p1; p1 := ithprime(n): if ts_num_midpal(p1) = 0 then return (p1) fi end: apranpal := [seq(ts_pra_n_pal(i), i=1..100000)]: apranpal;
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CROSSREFS
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Cf. A002385, A069217.
Sequence in context: A067860 A140037 A107209 this_sequence A045978 A141913 A100775
Adjacent sequences: A076610 A076611 A076612 this_sequence A076614 A076615 A076616
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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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