OFFSET
1,1
COMMENTS
EXAMPLE
MATHEMATICA
d[0] = d[1] = 0; d[n_] := n*Plus @@ ((Last[#]/First[#]) & /@ FactorInteger[n]); curzonQ[n_] := PowerMod[2, n, 2*n + 1] == 2*n; Select[Range[2, 1050], curzonQ[#] && curzonQ[d[#]] &] (* Amiram Eldar, May 05 2023 *)
PROG
(Magma) czn:=func<n|(2^n+1) mod (2*n+1) eq 0>; f:=func<n |n le 1 select 0 else
n*(&+[Factorisation(n)[i][2] / Factorisation(n)[i][1]: i in
[1..#Factorisation(n)]])>; [n:n in [2..5000]|czn(n) and czn(Floor(f(n)))];
CROSSREFS
KEYWORD
nonn
AUTHOR
Marius A. Burtea, May 03 2023
STATUS
approved