The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 R. J. Mathar, Table of n, a(n) for n = 1..1000 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 Adjacent sequences: A049602 A049603 A049604 * A049606 A049607 A049608 KEYWORD easy,nonn AUTHOR Benoit Cloitre, Jul 26 2002 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

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