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 A124874 Number of distinct primes dividing A007408(n). 1
 0, 1, 1, 3, 2, 3, 3, 2, 3, 4, 3, 2, 3, 2, 1, 3, 2, 4, 1, 3, 2, 5, 2, 4, 2, 1, 3, 4, 3, 5, 1, 2, 3, 2, 3, 8, 4, 4, 5, 4, 8, 6, 7, 2, 4, 6, 3, 2, 4, 3, 2, 4, 3, 4, 2, 8, 3, 3, 4, 4, 3, 3, 7, 2, 5, 9, 4, 2, 6, 7, 3, 5, 6, 4, 3, 6, 4, 6, 4, 4, 3, 3, 8, 5, 7, 4, 5 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 LINKS Amiram Eldar, Table of n, a(n) for n = 1..106 FORMULA a(n) = A001221(A007408(n)). EXAMPLE a(1) = 0 since no prime divides A007408(1) = 1, a(2) = 1 since 3 is the only prime dividing A007408(2) = 9, a(3) = 1 since A007408(3) = 251 is prime, a(4) = 3 since A007408(4) = 5 * 11 * 37, a(6) = 3 since 7, 11, 53 are the only primes dividing A007408(6) = 7^2 * 11 * 53. MAPLE seq( (nops@op)(2, (ifactors@A007408)(n)), n=1..25); MATHEMATICA Table[PrimeNu[Numerator[Sum[1/k^3, {k, 1, n}]]], {n, 1, 50}] (* Amiram Eldar, Feb 09 2020 *) CROSSREFS Cf. A001221, A007408, A124876, A124877. Sequence in context: A054263 A308656 A178775 * A230258 A016459 A242309 Adjacent sequences:  A124871 A124872 A124873 * A124875 A124876 A124877 KEYWORD nonn AUTHOR M. F. Hasler, Nov 11 2006 EXTENSIONS More terms from Amiram Eldar, Feb 09 2020 STATUS approved

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Last modified March 28 20:01 EDT 2020. Contains 333103 sequences. (Running on oeis4.)