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A174824
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a(n) = period of the sequence {m^m, m >= 1} modulo n.
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20
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1, 2, 6, 4, 20, 6, 42, 8, 18, 20, 110, 12, 156, 42, 60, 16, 272, 18, 342, 20, 42, 110, 506, 24, 100, 156, 54, 84, 812, 60, 930, 32, 330, 272, 420, 36, 1332, 342, 156, 40, 1640, 42, 1806, 220, 180, 506, 2162, 48, 294, 100, 816, 156, 2756, 54, 220, 168, 342
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OFFSET
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1,2
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COMMENTS
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This is a divisibility sequence: if n divides m, a(n) divides a(m).
We have the equality n = a(n) for numbers n in A124240, which is related to Carmichael's function (A002322). The largest values of a(n) occur when n is prime, in which case a(n) = n*(n-1). - T. D. Noe, Feb 21 2014
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LINKS
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FORMULA
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If n and m are relatively prime, a(n*m) = lcm(a(n), a(m)); a(p^k) = (p-1)*p^k for p prime and k > 0.
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EXAMPLE
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For n=3, 1^1 == 1 (mod 3), 2^2 == 1 (mod 3), 3^3 == 0 (mod 3), etc. The sequence of residues 1, 1, 0, 1, 2, 0, 1, 1, 0, ... has period 6, so a(3) = 6. - Michael B. Porter, Mar 13 2018
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MATHEMATICA
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Table[LCM[n, CarmichaelLambda[n]], {n, 100}] (* T. D. Noe, Feb 20 2014 *)
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PROG
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(PARI) a(n)=local(ps); ps=factor(n)[, 1]~; for(k=1, #ps, n=lcm(n, ps[k]-1)); n
(PARI) apply( {A174824(n)=lcm(lcm([p-1|p<-factor(n)[, 1]]), n)}, [1..99]) \\ [...] = znstar(n)[2], but 3x faster. - M. F. Hasler, Nov 13 2019
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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