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 A078120 Number of distinct prime divisors of n-th balanced number. 1
 0, 1, 1, 2, 2, 2, 2, 3, 2, 3, 2, 3, 3, 3, 3, 3, 3, 4, 2, 3, 3, 3, 3, 4, 4, 3, 3, 4, 4, 3, 3, 4, 4, 3, 3, 4, 3, 3, 4, 4, 3, 3, 4, 4, 5, 4, 4, 4, 3, 3, 4, 4, 3, 2, 4, 4, 4, 4, 3, 4, 3, 4, 4, 5, 4, 4, 4, 3, 4, 3, 4, 4, 5, 4, 4, 4, 4, 4, 4, 5, 3, 4, 5, 4, 5, 5, 4, 5, 4, 4, 4, 5, 4, 4, 5, 4, 4, 3, 5, 5, 4, 4, 5, 4, 4 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 FORMULA a(n) = A001221(A020492(n)). EXAMPLE The 575th balanced number is 2089542 = 2*3*7*13*43*89, so a(575)=6; sigma(2089542)/phi(2089542) = 10. MATHEMATICA PrimeNu /@ Select[Range[10^5], Divisible[DivisorSigma[1, #], EulerPhi[#]] &] (* Amiram Eldar, Dec 05 2019 *) CROSSREFS Cf. A020492, A001221. Sequence in context: A163374 A108502 A260235 * A057525 A331362 A139325 Adjacent sequences: A078117 A078118 A078119 * A078121 A078122 A078123 KEYWORD nonn AUTHOR Labos Elemer, Dec 06 2002 STATUS approved

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Last modified March 5 05:10 EST 2024. Contains 370537 sequences. (Running on oeis4.)