OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
a(1) = 144 since sigma(66) = 144 > 2*66 = 132.
MAPLE
with(numtheory); egcd := proc(n::posint) local L; if n>1 then L:=ifactors(n)[2]; L:=map(z->z[2], L); return igcd(op(L)) else return 1 fi; end; L:=[]: P:={}: for w to 1 do for n from 1 to 10000 do s:=sigma(n); if s>2*n and egcd(s)>1 then print(n, s, ifactor(s)); L:=[op(L), n]; P:=P union {s}; fi od od; L; P;
MATHEMATICA
ppQ[n_] := GCD @@ FactorInteger[n][[;; , 2]] > 1;
f[n_] := Module[{s = DivisorSigma[1, n]}, If[s > 2*n, s, Nothing]];
seq[max_] := Union[Select[Array[f, max], # < max && ppQ[#] &]]; seq[60000] (* Amiram Eldar, Mar 11 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Walter Kehowski, Dec 01 2006
EXTENSIONS
a(32) inserted and more terms added by Amiram Eldar, Mar 11 2024
STATUS
approved