A337189 Numbers k such that k divides A340180(k).

1, 2, 3, 7, 61, 75, 104, 2097, 3304, 7320, 42104, 280586

Offset: 1

Author

J. M. Bergot and Robert Israel, Jan 29 2021

Keywords

• nonn
• more

Examples

			a(4) = 61 is a term because A340180(61) = 671 = 11*61.
		

Crossrefs

Cf. A340180.

Programs

Maple

f := proc(n)
local t, s, k;
    s := numtheory:-sigma(n);
    t := 0;
    for k to n - 1 do if igcd(n, k) = 1 then t := t + (s mod k) end if
    end do;
    t
end proc:
select(t -> f(t) mod t = 0, [$1..10000]);

Mathematica

f[n_] := Mod[DivisorSigma[1, n], Select[Range[n-1], CoprimeQ[#, n]&]] // Total;
Select[Range[300000], If[Divisible[f[#], #], Print[#]; True, False]&] (* Jean-François Alcover, Jan 31 2021 *)

Extensions

a(12) from Jean-François Alcover, Feb 01 2021