OFFSET
1,1
COMMENTS
Corresponding values of n are in A187086. A048050 is Chowla's function: sum of divisors of n except 1 and n.
By the Goldbach conjecture, every even square appears; take two odd primes p and q such that p+q = k^2, then Chowla function of p*q is k^2. It appears that 17^2 is the first odd square not in A048050.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
chowla[n_] := DivisorSigma[1, n] - n - 1; s = {}; Do[c = chowla[n]; If[c > 0 && IntegerQ@Sqrt[c], AppendTo[s, c]], {n, 1, 10^3}]; s (* Amiram Eldar, Aug 28 2019 *)
PROG
(PARI) {for(n=1, 2000, spf=sumdiv(n, x, x)-1-n; if(spf>0&&issquare(spf), print1(spf", ")))}
(Magma) A048050:=func< n | n eq 1 or IsPrime(n) select 0 else &+[ a: a in Divisors(n) | a ne 1 and a ne n ] >; [ a: n in [1..2500] | a gt 0 and IsSquare(a) where a is A048050(n) ]; // Klaus Brockhaus, Mar 04 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, Mar 04 2011
STATUS
approved