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A049605
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Smallest k>1 such that k divides sigma(k*n).
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4
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6, 3, 2, 6, 2, 2, 2, 3, 6, 2, 2, 2, 2, 2, 2, 6, 2, 3, 2, 2, 2, 2, 2, 2, 6, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 6, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 6, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 6, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 6, 2, 2, 2, 2, 2
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OFFSET
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1,1
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COMMENTS
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a(n) = 2, 3 or 6. For any m, a(A028983(m)) = 2. If a(m)=6 then m is a square but if m is a square a(m) is not necessarily 6, first example is 7: a(7^2)=3 (cf. A072864).
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LINKS
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MAPLE
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for k from 2 do
if modp(numtheory[sigma](k*n), k) = 0 then
return k;
end if;
end do:
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MATHEMATICA
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sk[n_]:=Module[{k=2}, While[!Divisible[DivisorSigma[1, k*n], k], k++]; k]; sk /@ Range[110] (* Harvey P. Dale, Jan 04 2015 *)
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PROG
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(PARI) a(n) = {k = 2; while(sigma(k*n) % k, k++); k ; } \\ Michel Marcus, Nov 21 2013
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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