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 A138011 a(n) = number of positive divisors, k, of n where d(k) divides d(n). (d(m) = number of positive divisors of m.). 3
 1, 2, 2, 2, 2, 4, 2, 3, 2, 4, 2, 5, 2, 4, 4, 2, 2, 5, 2, 5, 4, 4, 2, 6, 2, 4, 3, 5, 2, 8, 2, 4, 4, 4, 4, 4, 2, 4, 4, 6, 2, 8, 2, 5, 5, 4, 2, 5, 2, 5, 4, 5, 2, 6, 4, 6, 4, 4, 2, 11, 2, 4, 5, 2, 4, 8, 2, 5, 4, 8, 2, 10, 2, 4, 5, 5, 4, 8, 2, 5, 2, 4, 2, 11, 4, 4, 4, 6, 2, 11, 4, 5, 4, 4, 4, 9, 2, 5, 5, 4 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS EXAMPLE 12 has 6 divisors (1,2,3,4,6,12). The number of divisors of each of these divisors of 12 form the sequence (1,2,2,3,4,6). Of these, five divide d(12)=6: 1,2,2,3,6. So a(12) = 5. MATHEMATICA Table[Length[Select[Divisors[n], Mod[Length[Divisors[n]], Length[Divisors[ # ]]] == 0 &]], {n, 1, 100}] - Stefan Steinerberger, Feb 29 2008 CROSSREFS Cf. A138010, A138012. Sequence in context: A098219 A173439 A061389 * A036555 A046927 A084718 Adjacent sequences:  A138008 A138009 A138010 * A138012 A138013 A138014 KEYWORD nonn AUTHOR Leroy Quet Feb 27 2008 EXTENSIONS More terms from Stefan Steinerberger, Feb 29 2008 STATUS approved

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