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A005091
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Number of distinct primes = 3 mod 4 dividing n.
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4
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,21
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FORMULA
| Additive with a(p^e) = 1 if p = 3 (mod 4), 0 otherwise.
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MATHEMATICA
| 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
| (PARI) for(n=1, 100, print1(sumdiv(n, d, isprime(d)*if((d-3)%4, 0, 1)), ", "))
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CROSSREFS
| Cf. A001221, A005089.
Sequence in context: A077267 A134022 A085975 * A086831 A191340 A111405
Adjacent sequences: A005088 A005089 A005090 * A005092 A005093 A005094
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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