cp's OEIS Frontend

A076520 n appears once if n is the sum of 2 nonzero squares in 1 way, twice if n is the sum of 2 squares in 2 ways, 3 times if n is the sum of 2 squares 3 ways etc.

%I A076520 #28 Dec 01 2013 13:08:07
%S A076520 2,5,5,8,10,10,13,13,17,17,18,20,20,25,25,26,26,29,29,32,34,34,37,37,
%T A076520 40,40,41,41,45,45,50,50,50,52,52,53,53,58,58,61,61,65,65,65,65,68,68,
%U A076520 72,73,73,74,74,80,80,82,82,85,85,85,85,89,89,90,90,97,97,98,100,100
%N A076520 n appears once if n is the sum of 2 nonzero squares in 1 way, twice if n is the sum of 2 squares in 2 ways, 3 times if n is the sum of 2 squares 3 ways etc.
%H A076520 <a href="/index/Su#ssq">Index entries for sequences related to sums of squares</a>
%F A076520 Does limit n -> infinity a(n)/n exist?
%F A076520 Answer: Yes, and it is equal to 4/Pi. - _Charles R Greathouse IV_, Dec 01 2013
%o A076520 (PARI) lista(nn) = for (n=1, nn, for (i=1, n-1, if (issquare(i) && issquare(n-i), print1(n, ", ")))) \\ _Michel Marcus_, Nov 30 2013
%o A076520 (PARI) list(lim)=my(v=List());for(n=2,lim,for(k=1,sqrtint(n-1),if(issquare(n-k^2),listput(v,n))));Vec(v) \\ _Charles R Greathouse IV_, Dec 01 2013
%Y A076520 Cf. A000404, A001105, A025285, A025302.
%K A076520 nonn
%O A076520 1,1
%A A076520 _Benoit Cloitre_, Nov 09 2002
%E A076520 Typo in definition corrected by _Michel Marcus_, Dec 01 2013