A386390 Numbers k such that k-1 | sigma+(k) where sigma+ is A107758.

2, 6, 66, 225, 8646, 101025, 149497986, 20412000225

Offset: 1

Author

Michel Marcus, Aug 20 2025

Keywords

• nonn
• more
• new

Crossrefs

Cf. A107758, A055708.

Programs

Mathematica

a107758[n_]:=DivisorSum[n, DivisorSigma[1, #] &, CoprimeQ[n/#, #] &];Select[Range[2,10^6],Divisible[a107758[#],#-1]&] (* James C. McMahon, Aug 21 2025 *)

PARI

isok(k) = if (k>1, !(sumdiv(k, d, if(gcd(k/d, d) == 1, sigma(d))) % (k-1)));

Extensions

a(8) from Vincenzo Librandi, Aug 21 2025