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Search: id:A113030
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| A113030 |
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Largest prime arising that can be formed by stringing together the decimal expansions of some or all of the first n numbers in some order. |
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+0
1
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| 2, 31, 4231, 5431, 65423, 7652413, 8765423, 98765431, 10987653421, 111098765423, 12111098765413, 13121110987654231, 141312111098765213, 15141312111098763241, 16151413121110987654213, 171615141312111098764523
(list; graph; listen)
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OFFSET
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2,1
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EXAMPLE
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a(3) = 31 as 321 or any other three digit permutation is not a prime and 23 < 31. Any permutation of all or a few of the first five numbers 1,2,3,4,5,gives the largest prime 5431. Hence a(5) = 5431.
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MATHEMATICA
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for 4<n<20 (* first do *) Needs["DiscreteMath`Combinatorica`"] (* then *) f[n_] := Block[{a = Flatten@IntegerDigits@Range[n, 6, -1], b = Flatten[ Permutations /@ Flatten[ Table[ KSubsets[ Range@5, i], {i, 5}], 1], 1], t = {}}, Do[AppendTo[t, Join[a, b[[k]] ]], {k, 325}]; Max@Select[FromDigits /@ t, PrimeQ[ # ] &]]; Table[ f[n], {n, 5, 18}] (* Robert G. Wilson v *)
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CROSSREFS
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Sequence in context: A010789 A134646 A004072 this_sequence A030001 A018802 A004842
Adjacent sequences: A113027 A113028 A113029 this_sequence A113031 A113032 A113033
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KEYWORD
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base,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Jan 03 2006
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EXTENSIONS
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a(7)-a(18) from Robert G. Wilson v (rgwv(at)rgwv.com), Jan 11 2006
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