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A127817
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a(n) = least k such that the remainder when 9^k is divided by k is n.
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46
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2, 7, 6, 5, 38, 723, 74, 2592842671511, 11, 3827, 14, 717, 34, 59035, 21, 259, 152, 237, 62, 626131, 30, 169, 58, 25, 56, 1921, 39, 361, 65, 49, 63010, 287, 48, 55, 46, 63, 932, 3786791, 69, 69637, 230, 221, 6707, 1057, 57, 4907, 253, 681, 148, 393217991, 70
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OFFSET
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1,1
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LINKS
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EXAMPLE
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For n=4, since 9^5 == 4 (mod 5) and 9^k is not congruent to 4 (mod k) for any k < 5, a(4) = 5. Michael B. Porter, Dec 10 2016
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MAPLE
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a127817 := [seq(0, j=1..nmax)] ; for k from 1 do n := modp(9^k, k) ; if n > 0 and n <= nmax then if op(n, a127817) = 0 then a127817 := subsop(n=k, a127817) ; print( op(1..50, a127817) ) ; fi; fi; od: # R. J. Mathar, Jul 16 2009
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MATHEMATICA
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t = Table[0, {10000}]; k = 1; lst = {}; While[k < 4500000000, a = PowerMod[9, k, k]; If[ a<10001 && t[[a]]==0, t[[a]]=k; Print[{a, k}]]; k++ ]; t
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CROSSREFS
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Cf. A036236, A078457, A119678, A119679, A127816, A119715, A119714, A127818, A127819, A127820, A127821.
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KEYWORD
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hard,nonn
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AUTHOR
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EXTENSIONS
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a(8) <= 2592842671511 from Joe K. Crump (joecr(AT)carolina.rr.com), Feb 06 2007
I changed the Mathematica coding to reflect the current limits Robert G. Wilson v, Jul 18 2009
Value for a(8) as suggested by J. K. Crump confirmed by Hagen von Eitzen, Jul 21 2009
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STATUS
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approved
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