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A005091
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Number of distinct primes = 3 mod 4 dividing n.
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11
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0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1, 1, 0, 0, 1, 1, 0, 2, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 0, 2, 0, 1, 1, 0, 1, 1, 0, 0, 2, 1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 2, 0, 1, 1, 0, 1, 2, 0, 0, 2, 1, 0, 2, 1, 1, 1, 0, 0, 1, 1, 2, 1, 1, 0, 1, 0, 1, 2, 0, 1, 1, 1, 0, 1, 1, 1, 2, 1, 1, 1, 0, 1, 2, 0, 0, 1
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OFFSET
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1,21
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LINKS
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FORMULA
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Additive with a(p^e) = 1 if p = 3 (mod 4), 0 otherwise.
a(n) = Sum_{p|n} (binomial(p,3) mod 2), where p is a prime. - Ridouane Oudra, Nov 19 2019
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MAPLE
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with(numtheory): seq(add(binomial(p, 3) mod 2, p in factorset(n)), n=1..100); # Ridouane Oudra, Nov 19 2019
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MATHEMATICA
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f[n_]:=Length@Select[If[n==1, {}, FactorInteger[n]], Mod[#[[1]], 4]==3&]; Table[f[n], {n, 102}] (* Ray Chandler, Dec 18 2011 *)
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PROG
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(PARI) for(n=1, 100, print1(sumdiv(n, d, isprime(d)*if((d-3)%4, 0, 1)), ", "))
(Haskell)
a005091 = sum . map a079261 . a027748_row
(Magma) [0] cat [#[p:p in PrimeDivisors(n)| p mod 4 eq 3]: n in [2..100]]; // Marius A. Burtea, Nov 19 2019
(Magma) [0] cat [&+[Binomial(p, 3) mod 2:p in PrimeDivisors(n)]:n in [2..100]]; // Marius A. Burtea, Nov 19 2019
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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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