OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..2256 (terms below 30000)
MATHEMATICA
fun[p_, e_] := Module[{b = IntegerDigits[e, 2]}, m = Length[b]; Product[If[b[[j]] > 0, 1 + p^(2^(m - j)), 1], {j, 1, m}]]; isigma[1] = 1; isigma[n_] := isigma[n] = Times @@ (fun @@@ FactorInteger[n]); untouchableQ[n_] := Catch[ Do[ If[n == isigma[k]-k, Throw[True]], {k, 0, (n-1)^2}]] === Null; Reap[ Table[ If[ untouchableQ[n], Sow[n]], {n, 2, 1000}]][[2, 1]] (* after Jean-François Alcover at A005114 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Feb 20 2019
STATUS
approved