OFFSET
1,1
LINKS
Sam Wagstaff, Cunningham Project, Factorizations of 10^n-1, n odd, n<300
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
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Sep 10 2001
EXTENSIONS
a(62)-a(82) from Giovanni Resta, Jun 26 2018
STATUS
approved