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A345219
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Number of divisors of n with an odd number of primes not exceeding them.
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1
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0, 1, 0, 1, 1, 2, 0, 1, 0, 2, 1, 3, 0, 1, 1, 1, 1, 3, 0, 2, 0, 2, 1, 4, 2, 2, 1, 2, 0, 3, 1, 2, 2, 3, 2, 5, 0, 1, 0, 2, 1, 3, 0, 2, 1, 2, 1, 5, 1, 4, 2, 3, 0, 4, 2, 2, 0, 1, 1, 5, 0, 2, 0, 2, 1, 4, 1, 4, 2, 4, 0, 6, 1, 2, 3, 2, 2, 4, 0, 2, 1, 2, 1, 6, 3, 2, 1, 3, 0, 4, 0, 2, 1
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OFFSET
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1,6
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LINKS
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FORMULA
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a(n) = Sum_{d|n} (pi(d) mod 2).
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EXAMPLE
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a(24) = 4; The divisors d of 24 are: 1, 2, 3, 4, 6, 8, 12, 24 and the corresponding values of pi(d) are: 0, 1, 2, 2, 3, 4, 5, 9. There are 4 odd values of pi(d).
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MATHEMATICA
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Table[Sum[Mod[PrimePi[k], 2] (1 - Ceiling[n/k] + Floor[n/k]), {k, n}], {n, 100}]
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PROG
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(PARI) a(n) = sumdiv(n, d, primepi(d) % 2); \\ Michel Marcus, Jun 11 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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