OFFSET
1,1
COMMENTS
It is conjectured that if m is not a sum of 2 squares (i.e., m is in A022544(k)) sigma(m) == 0 (mod 4).
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[10^3], And[SquaresR[2, #] > 0, Divisible[DivisorSigma[1, #], 4]] &] (* Michael De Vlieger, Jul 30 2017 *)
PROG
(PARI) for(n=1, 1000, if(1-sign(sum(i=0, n, sum(j=0, i, if(i^2+j^2-n, 0, 1))))+sigma(n)%4==0, print1(n, ", ")))
(Python)
from math import prod
from itertools import count, islice
from sympy import factorint
def A071011_gen(): # generator of terms
return filter(lambda n:(lambda f:all(p & 3 != 3 or e & 1 == 0 for p, e in f) and prod((p**(e+1)-1)//(p-1) & 3 for p, e in f) & 3 == 0)(factorint(n).items()), count(0))
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, May 19 2002
STATUS
approved