A216415 a(n) = smallest positive m such that 2n-1 | 10^m-1, or 0 if no such m exists.

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

Offset: 1

Author

V. Raman, Sep 07 2012

Keywords

• nonn

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.

Crossrefs

Cf. A002326, A002329, A007732, A070682, A084680. - N. J. A. Sloane, Sep 08 2012

Programs

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