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A099679
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Least m such that repunit R_m is a multiple of A045572(n) (i.e. odd numbers not divisible by 5).
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2
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1, 3, 6, 9, 2, 6, 16, 18, 6, 22, 27, 28, 15, 6, 3, 6, 5, 21, 46, 42, 48, 13, 18, 58, 60, 18, 33, 66, 35, 8, 6, 13, 81, 41, 84, 44, 6, 15, 96, 18, 4, 34, 53, 108, 3, 112, 18, 48, 22, 15, 42, 21, 130, 18, 8, 46, 138, 6, 42, 148, 75, 144, 78, 39, 66, 81, 166, 78, 18, 43, 174, 178
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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LINKS
| P. de Geest, Repunits and their prime factors
T. Granlund, Factors of 10^n - 1
M. Kamada, Factorizations of 11...11(Repunits)
Y. Koide, Factorization of Repunit Numbers
P. Yiu, Factorization of Repunits R_n for n=<50, Appendix Chap. 18.5 pp. 173/360 in 'Recreational Mathematics'.
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
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MATHEMATICA
| f[n_] := Block[{k = 1}, While[ Mod[(10^k - 1)/9, n] != 0, k++ ]; k]; f /@ Select[ 2Range[ 90] - 1, Mod[ #, 5] != 0 &] (from Robert G. Wilson v Oct 27 2004)
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PROG
| (PARI) A(n)={ \\ Least m such that n | R_m
my(f=factor(n), s=1, t);
for(i=1, #f[, 1],
if(f[i, 1]==3,
t=3
,
t=Mod(10, 9*f[i, 1]);
fordiv(f[i, 1]-1, d,
if(t^d==1, t=d; break)
)
);
t*=f[i, 1]^(f[i, 2]-1);
s=lcm(s, t)
);
s
};
a(n)=A(10*(n>>2)+[-1, 1, 3, 7][n%4+1]) \\ Least m such that A045572(n) | R_m
\\ Charles R Greathouse IV, Jul 31 2011
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CROSSREFS
| Cf. A002275, A045572.
Sequence in context: A131579 A059626 A094561 * A013663 A180593 A195771
Adjacent sequences: A099676 A099677 A099678 * A099680 A099681 A099682
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KEYWORD
| nonn,easy
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AUTHOR
| Lekraj Beedassy (blekraj(AT)yahoo.com), Oct 26 2004
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EXTENSIONS
| Corrected and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), Oct 27 2004
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