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A050460
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a(n) = Sum_{d|n, n/d=1 mod 4} d.
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11
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1, 2, 3, 4, 6, 6, 7, 8, 10, 12, 11, 12, 14, 14, 18, 16, 18, 20, 19, 24, 22, 22, 23, 24, 31, 28, 30, 28, 30, 36, 31, 32, 34, 36, 42, 40, 38, 38, 42, 48, 42, 44, 43, 44, 60, 46, 47, 48, 50, 62, 54, 56, 54, 60, 66, 56, 58, 60, 59, 72, 62, 62, 73, 64, 84, 68
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OFFSET
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1,2
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COMMENTS
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Not multiplicative: a(3)*a(7) <> a(21), for example.
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LINKS
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FORMULA
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G.f.: Sum_{k>0} x^(4*k-3) / (1 - x^(4*k-3))^2. - Seiichi Manyama, Jun 29 2023
Sum_{k=1..n} a(k) ~ c * n^2 / 2, where c = A222183. (End)
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MAPLE
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a := 0 ;
for d in numtheory[divisors](n) do
if (n/d) mod 4 = 1 then
a := a+d ;
end if;
end do:
a;
end proc:
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MATHEMATICA
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a[n_] := DivisorSum[n, Boole[Mod[n/#, 4] == 1]*#&]; Array[a, 70] (* Jean-François Alcover, Dec 01 2015 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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