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A216473
a(n) = smallest m such that 2n-1 | (10^m-1)/9, or 0 if no such m exists.
2
1, 3, 0, 6, 9, 2, 6, 0, 16, 18, 6, 22, 0, 27, 28, 15, 6, 0, 3, 6, 5, 21, 0, 46, 42, 48, 13, 0, 18, 58, 60, 18, 0, 33, 66, 35, 8, 0, 6, 13, 81, 41, 0, 84, 44, 6, 15, 0, 96, 18, 4, 34, 0, 53, 108, 3, 112, 0, 18, 48, 22, 15, 0, 42, 21, 130, 18, 0, 8, 46, 138, 6, 0
OFFSET
1,2
COMMENTS
a(n) is the multiplicative order of 10 mod 9*(2n-1) if defined, otherwise 0.
MATHEMATICA
Table[s = MultiplicativeOrder[10, 9*(2*n - 1)]; If[! IntegerQ[s], 0, s], {n, 100}] (* T. D. Noe, Sep 20 2012 *)
PROG
(PARI) A216473(n)=if(n%5-3, znorder(Mod(10, 18*n-9))) \\ M. F. Hasler, Sep 29 2012
(PARI) for(i=0, 200, i++; if(i%5==0, print1(0", "), print1(znorder(Mod(10, 9*i))", "))) \\ V. Raman, Nov 22 2012
(PARI) for(i=0, 200, i++; m=0; for(x=1, i, if(((10^x-1)/9)%i==0, m=x; break)); print1(m", ")) \\ V. Raman, Nov 22 2012
CROSSREFS
Cf. A002326.
Sequence in context: A321482 A182042 A011415 * A198433 A141434 A077911
KEYWORD
nonn
AUTHOR
V. Raman, Sep 07 2012
EXTENSIONS
Definition corrected by V. Raman, Sep 20 2012
STATUS
approved