OFFSET
1,1
COMMENTS
Numbers m such that A129294(m) = #{1,m-1} = 2.
Essentially the same as A096175. Note that m^3 - 1 = (m - 1)*(m^2 + m + 1), so m - 1 must be prime. For m > 4, the smallest divisor > 1 of m^2 + m + 1 is no larger than sqrt(m^2 + m + 1) < m + 1 unless m^2 + m + 1 is also prime. Also note that gcd(m, m^2 + m 1 ) = gcd(m - 1, m^2 + m + 1) = 1, so m^2 + m + 1 must also be prime, making m^3 - 1 a semiprime. - Jianing Song, Aug 01 2018
FORMULA
a(n) = A096175(n-2) for n > 2. - Jianing Song, Aug 01 2018
EXAMPLE
{1,11,157,1727} is the set of divisors of 12^3 - 1, therefore 12 is a term, since A129294(12) = #{1,11} = 2.
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Apr 09 2007
STATUS
approved