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A350331
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Number of divisors of n that are prime or the product of 2 (not necessarily distinct) primes.
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2
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0, 1, 1, 2, 1, 3, 1, 2, 2, 3, 1, 4, 1, 3, 3, 2, 1, 4, 1, 4, 3, 3, 1, 4, 2, 3, 2, 4, 1, 6, 1, 2, 3, 3, 3, 5, 1, 3, 3, 4, 1, 6, 1, 4, 4, 3, 1, 4, 2, 4, 3, 4, 1, 4, 3, 4, 3, 3, 1, 7, 1, 3, 4, 2, 3, 6, 1, 4, 3, 6, 1, 5, 1, 3, 4, 4, 3, 6, 1, 4, 2, 3, 1, 7, 3, 3, 3, 4, 1, 7, 3, 4
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OFFSET
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1,4
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COMMENTS
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Number of divisors of n of the form p, p^2, or p*q, where p and q are prime.
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LINKS
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FORMULA
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MATHEMATICA
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a[1] = 0; a[n_] := Module[{e = FactorInteger[n][[;; , 2]]}, Total[Min[#, 2] & /@ e] + Binomial[Length[e], 2]]; Array[a, 100] (* Amiram Eldar, Dec 25 2021 *)
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PROG
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(PARI) a(n) = sumdiv(n, d, isprime(d) || (bigomega(d)==2)); \\ Michel Marcus, Dec 25 2021
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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