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Search: id:A156770
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| A156770 |
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1 then least greater integer such that concatenate a(n-1),a(n) and concatenate a(n),a(n+1) are both prime. |
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+0
1
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| 1, 3, 7, 9, 11, 17, 21, 29, 39, 43, 49, 51, 53, 81, 91, 99, 103, 123, 127, 133, 153, 191, 227, 231, 241, 249, 253, 273, 281, 291, 293, 311, 323, 333, 337, 339, 341, 347, 359, 377, 387, 397, 427, 429, 431, 441, 443, 453, 461, 467, 471, 481, 489, 493, 523, 541
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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17, 29 and 39 are in as 1729 & 2939 are prime.
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MAPLE
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cat2 := proc(a, b) a*10^(max(1, ilog10(b)+1))+b ; end: A156770 := proc(n) option remember ; local a; if n = 1 then 1; else for a from procname(n-1)+1 do if isprime( cat2(procname(n-1), a) ) then RETURN(a) ; fi; od: fi; end: seq(A156770(n), n=1..80) ; [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Feb 20 2009]
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CROSSREFS
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Sequence in context: A125667 A072939 A075607 this_sequence A088630 A129747 A004614
Adjacent sequences: A156767 A156768 A156769 this_sequence A156771 A156772 A156773
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KEYWORD
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nonn,base
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AUTHOR
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Gerald Hillier (adr.rabbicat(AT)gmail.com), Feb 15 2009
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Feb 20 2009
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