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Search: id:A090841
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| A090841 |
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Smallest prime whose product of digits is 7^n. |
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+0
6
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| 11, 7, 11177, 1777, 71777, 1777717, 1177717771, 77777177, 7177717777, 1777777777, 71777777777, 1717777777777, 7177777777777, 17777777777777, 17177777777777717, 7717777777777777, 1177777777177777777
(list; graph; listen)
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OFFSET
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0,1
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EXAMPLE
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a(6) = 1177717771 because its digital product is 7^6.
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MATHEMATICA
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NextPrim[n_] := Block[{k = n + 1}, While[ !PrimeQ[k], k++ ]; k]; a = Table[0, {18}]; p = 2; Do[q = Log[7, Times @@ IntegerDigits[p]]; If[q != 0 && IntegerQ[q] && a[[q]] == 0, a[[q]] = p; Print[q, " = ", p]]; p = NextPrim[p], {n, 1, 10^9}]
For a(8); a = Map[ FromDigits, Permutations[{1, 1, 7, 7, 7, 7, 7, 7, 7, 7}]]; Min[ Select[a, PrimeQ[ # ] &]]
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CROSSREFS
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Cf. A089365, A088653, A090840, A091465, A089298.
Sequence in context: A002749 A055505 A159526 this_sequence A085757 A003567 A085688
Adjacent sequences: A090838 A090839 A090840 this_sequence A090842 A090843 A090844
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KEYWORD
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base,nonn
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AUTHOR
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Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 09 2003
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