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A049605 Smallest k>1 such that k divides sigma(k*n). 4
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
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).
LINKS
MAPLE
A049605 := proc(n)
for k from 2 do
if modp(numtheory[sigma](k*n), k) = 0 then
return k;
end if;
end do:
end proc: # R. J. Mathar, Oct 26 2015
MATHEMATICA
sk[n_]:=Module[{k=2}, While[!Divisible[DivisorSigma[1, k*n], k], k++]; k]; sk /@ Range[110] (* Harvey P. Dale, Jan 04 2015 *)
PROG
(PARI) a(n) = {k = 2; while(sigma(k*n) % k, k++); k ; } \\ Michel Marcus, Nov 21 2013
CROSSREFS
Cf. A028983 (locations of 2), A067051 (locations of 3), A072862 (locations of 6).
Sequence in context: A078333 A302852 A348694 * A088395 A272082 A283443
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Jul 26 2002
STATUS
approved

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Last modified June 21 19:43 EDT 2024. Contains 373558 sequences. (Running on oeis4.)