A064127 - OEIS

A064127

Number of divisors of 11^n - 1 that are relatively prime to 11^m - 1 for all 0 < m < n.

4, 2, 4, 2, 2, 2, 4, 2, 2, 2, 4, 4, 4, 2, 2, 4, 2, 2, 2, 2, 8, 16, 8, 4, 8, 8, 2, 8, 4, 4, 8, 4, 8, 8, 4, 2, 16, 16, 64, 4, 128, 2, 4, 4, 2, 16, 8, 16, 8, 4, 16, 2, 16, 4, 16, 16, 4, 8, 8, 2, 8, 16, 32, 8, 4, 16, 16, 16, 8, 48, 32, 8, 2, 4, 16, 4, 4, 8, 8, 4

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..80.

Sam Wagstaff, Cunningham Project, Factorizations of 11^n-1, n odd, n<240

MATHEMATICA

a = {1}; Do[ d = Divisors[ 11^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[ 11^n - 1 ] ][ [ 1 ] ] ] ] ], {n, 1, 42} ]

PROG

(PARI) a(n) = sumdiv(11^n-1, d, vecsum(vector(n-1, k, gcd(d, 11^k-1) == 1)) == n-1); \\ Michel Marcus, Jun 23 2018

CROSSREFS

Cf. A063982.

Sequence in context: A375087 A269592 A105256 * A178253 A209272 A105397

Adjacent sequences: A064124 A064125 A064126 * A064128 A064129 A064130

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Sep 10 2001

EXTENSIONS

a(43)-a(80) from Jon E. Schoenfield, Jun 23 2018

STATUS

approved