OFFSET
1,1
COMMENTS
Numbers k such that A002129(k) is a square.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
The divisors of 76 are { 1, 2, 4, 19, 38, 76}, and (2 + 4 + 38 + 76 ) - (1 + 19 ) = 10^2. Hence 76 is in the sequence.
MAPLE
with(numtheory):for n from 2 by 2 to 200 do:x:=divisors(n):n1:=nops(x):s1:=0:s2:=0:for m from 1 to n1 do:if irem(x[m], 2)=1 then s1:=s1+x[m]:else s2:=s2+x[m]:fi:od: z:=sqrt(s2-s1):if z=floor(z) then printf(`%d, `, n): else fi:od:
MATHEMATICA
f[p_, e_] := If[p == 2, 3 - 2^(e + 1) , (p^(e + 1) - 1)/(p - 1)]; aQ[n_] := IntegerQ[Sqrt[-Times @@ (f @@@ FactorInteger[n])]]; Select[Range[2, 3200], aQ] (* Amiram Eldar, Jul 20 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Sep 22 2011
STATUS
approved