A212795 - OEIS

%I #10 Sep 24 2016 15:56:06

%S 10,37,45,101,109,136,226,234,261,325,442,450,477,541,666,785,793,820,

%T 884,1009,1225,1297,1305,1332,1396,1521,1737,2026,2034,2061,2080,2125,

%U 2250,2466,2809,3026,3034,3061,3125,3250,3321,3466

%N Sums of squares of two distinct nonzero triangular numbers, i.e., of the form A000217(m)^2+A000217(n)^2, m>n>0.

%C From a(28) on, terms are no more in the lexicographic order of increasing (m, n).

%e A000217 = (0, 1, 3, 6, ...), thus

%e a(1)=3^2+1^2, a(2)=6^2+1^2, a(3)=6^2+3^2, ...,

%e a(28)=45^2+1^2, ..., a(31)=36^2+28^2.

%t With[{nn=50},Take[Union[Total/@Subsets[Accumulate[Range[nn]]^2,{2}]],nn]] (* _Harvey P. Dale_, Sep 24 2016 *)

%o (PARI) vecsort(select(concat(vector(10,i,vector(i-1,j,A000217(i)^2+ A000217(j)^2))),x->x<11^4/4))

%Y A subsequence of A004431.

%K nonn

%O 1,1

%A _M. F. Hasler_, May 27 2012