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 A216415 a(n) = smallest positive m such that 2n-1 | 10^m-1, or 0 if no such m exists. 2
 1, 1, 0, 6, 1, 2, 6, 0, 16, 18, 6, 22, 0, 3, 28, 15, 2, 0, 3, 6, 5, 21, 0, 46, 42, 16, 13, 0, 18, 58, 60, 6, 0, 33, 22, 35, 8, 0, 6, 13, 9, 41, 0, 28, 44, 6, 15, 0, 96, 2, 4, 34, 0, 53, 108, 3, 112, 0, 6, 48, 22, 5, 0, 42, 21, 130, 18, 0, 8, 46, 46, 6, 0, 42, 148, 75, 16, 0, 78, 13, 66, 81, 0, 166, 78, 18, 43, 0, 58, 178, 180, 60, 0, 16, 6, 95, 192, 0, 98, 99 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS This is yet another version of the sequences defined in A002329, A007732, A070682, A084680. - N. J. A. Sloane, Sep 08 2012 a(n) gives the multiplicative order of 10 mod (2n-1), if it is finite, or 0 if not defined. LINKS V. Raman, Table of n, a(n) for n = 1..100. PROG (PARI) for(i=0, 200, i++; if(i%5==0, print1(0", "), print1(znorder(Mod(10, i))", "))) \\ V. Raman, Nov 22 2012 (PARI) for(i=0, 200, i++; m=0; for(x=1, i, if(((10^x-1))%i==0, m=x; break)); print1(m", ")) \\ V. Raman, Nov 22 2012 CROSSREFS Cf. A002326, A002329, A007732, A070682, A084680. - N. J. A. Sloane, Sep 08 2012 Sequence in context: A220782 A274617 A070682 * A112828 A085766 A002329 Adjacent sequences:  A216412 A216413 A216414 * A216416 A216417 A216418 KEYWORD nonn AUTHOR V. Raman, Sep 07 2012 STATUS approved

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Last modified December 12 12:50 EST 2019. Contains 329958 sequences. (Running on oeis4.)