sum of 2 squares

[benoit]

Chers seqfans,

Are some of those claims correct ?

(i) n is a sum of 2 squares in exactly 1 way   <==>   sigma(n)>0 (mod4)

(ii) n is not the sum of 2 squares    ==>   sigma(n)==0 (mod4)   (  
sigma(n)>0 (mod4)  ==>   n is the sum of 2 squares.)

sequences concerned :

http://www.research.att.com/projects/OEIS?Anum=A000404
http://www.research.att.com/projects/OEIS?Anum=A025284
........


Thanks
Benoit
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