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Search: id:A125570
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| A125570 |
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Numbers n such [Sum(x=1,n,(x-1)*6^(x-1))/6] is prime. |
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+0
1
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| 3, 7, 8, 19, 69, 77, 104, 107, 162, 163, 399, 4787, 4818
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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No more terms through 10^4.
Note that Sum(x=1,n,(x-1)*6^(x-1))/6 = (6^(n-1)*(5*n-6)+1)/25. Therefore this sequence consists of such n that (6^(n-1)*(5*n-6)+1)/25 is prime. [From Max Alekseyev (maxal(AT)cs.ucsd.edu), Oct 18 2008]
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MATHEMATICA
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s = 0; Do[s += (x-1)*6^(x-1)/6; If[PrimeQ[s], Print[x]], {x, 10^4}]
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CROSSREFS
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Cf. A119529.
Sequence in context: A136136 A057548 A122227 this_sequence A037208 A102007 A105756
Adjacent sequences: A125567 A125568 A125569 this_sequence A125571 A125572 A125573
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KEYWORD
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hard,more,nonn
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AUTHOR
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Ryan Propper (rpropper(AT)stanford.edu), Jan 01 2007
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