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A064126
Number of divisors of 10^n - 1 that are relatively prime to 10^m - 1 for all 0 < m < n.
0
3, 2, 2, 2, 4, 4, 4, 4, 2, 2, 4, 2, 8, 2, 4, 4, 4, 4, 2, 4, 8, 8, 2, 2, 8, 4, 4, 8, 32, 8, 8, 32, 4, 8, 8, 2, 8, 2, 2, 4, 16, 8, 16, 8, 4, 16, 4, 2, 4, 8, 16, 4, 16, 4, 16, 4, 8, 4, 4, 8, 128, 2, 32, 16, 4, 4, 8, 8, 8, 4, 4, 8, 8, 8, 8, 4, 16, 16, 64, 4, 32, 4
OFFSET
1,1
MATHEMATICA
a = {1}; Do[ d = Divisors[ 10^n - 1 ]; l = Length[ d ]; c = 0; k = 1; While[ k < l + 1, If[ Union[ GCD[ a, d[ [ k ] ] ] ] == {1}, c++ ]; k++ ]; Print[ c ]; a = Union[ Flatten[ Append[ a, Transpose[ FactorInteger[ 10^n - 1 ] ][ [ 1 ] ] ] ] ], {n, 1, 61} ]
PROG
(PARI) a(n) = sumdiv(10^n-1, d, vecsum(vector(n-1, k, gcd(d, 10^k-1) == 1)) == n-1); \\ Michel Marcus, Jun 23 2018
CROSSREFS
Cf. A063982.
Sequence in context: A064123 A024703 A102845 * A175333 A130845 A134653
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Sep 10 2001
EXTENSIONS
a(62)-a(82) from Giovanni Resta, Jun 26 2018
STATUS
approved