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Search: id:A155081
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| A155081 |
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Primes n such that largest digit of cjncatenation of n and n-th prime is a prime. |
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1
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| 2, 3, 5, 7, 11, 31, 37, 47, 53, 67, 71, 73, 101, 113, 137, 173, 227, 233, 241, 257, 271, 307, 331, 347, 367, 521, 523, 557, 571, 577, 607, 613, 673, 727, 733, 743, 751, 1277, 1307, 1361, 1367, 1451, 1453, 1471, 1511, 1523, 1553, 1567, 1571, 1627, 1657, 1663
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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If n=2=prime and 3=prime(2), then concatenation=23(2<3=prime) and 2=a(1). If n=3=prime and 5=prime(3), then c0ncatenation=35(3<5=prime) and 3=a(2). If n=7=prime and 17=prime(7), then concatenation=717(1<7=7=prime) and 7=a(3), etc.
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MAPLE
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concat := proc (a, b) local bb: bb := nops(convert(b, base, 10)): 10^bb*a+b end proc: p := proc (n) local dig, ld: dig := convert(concat(n, ithprime(n)), base, 10): ld := max(seq(dig[j], j = 1 .. nops(dig))): if isprime(n) = true and isprime(ld) = true then n else end if end proc: seq(p(n), n = 1 .. 2000); [From Emeric Deutsch (deutsch(AT)duke.poly.edu), Jan 27 2009]
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CROSSREFS
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Cf. A000040.
Sequence in context: A028911 A028912 A075236 this_sequence A157158 A155833 A028867
Adjacent sequences: A155078 A155079 A155080 this_sequence A155082 A155083 A155084
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KEYWORD
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nonn,base
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AUTHOR
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Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Jan 19 2009
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EXTENSIONS
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Corrected (added 5, removed 19, 59) and extended by Emeric Deutsch (deutsch(AT)duke.poly.edu), Jan 27 2009
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