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Search: id:A123342
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| A123342 |
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Least m such that 2^n+5^m is prime. |
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+0
3
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| 0, 0, 0, 1, 0, 1, 2, 5, 0, 5, 2, 1, 4, 3, 6, 11, 0, 19, 14, 3, 2, 5, 2, 3, 16, 11, 66, 35, 4, 7, 122, 17, 14, 13, 2, 3, 4, 15, 34
(list; graph; listen)
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OFFSET
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0,7
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EXAMPLE
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a(0)=0 because 2^0+5^0=1+1=2 is prime,
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MATHEMATICA
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f[n_] := Block[{p = If[n < 3 || EvenQ@n, 0, 1]}, While[ !PrimeQ[5^p + 2^n ], p += 2 ]; p] ; Table[f@n, {n, 0, 38}] (* Robert G. Wilson v *)
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PROGRAM
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(PARI) for(n=0, 38, k=2^n; m=0; while(!isprime(k+5^m), m++); print1(m, ", ")) - (Klaus Brockhaus, Oct 15 2006)
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CROSSREFS
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Cf. A123252.
Sequence in context: A112695 A067881 A024714 this_sequence A058204 A090625 A021403
Adjacent sequences: A123339 A123340 A123341 this_sequence A123343 A123344 A123345
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KEYWORD
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nonn,hard
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), Oct 11 2006
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EXTENSIONS
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Entries through a(38) checked by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Oct 15 2006
a(39) > 21000, then the sequence continues: 4,3,22,29,10,29,6,1,4,5,38,..., . - Robert G. Wilson v (rgwv(AT)rgwv.com), Nov 14 2006
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