Number of subsets of {1..n} whose sum of squares of elements is a square.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =6a(5) =7a(6) =10a(7) =12a(8) =17a(9) =26a(10) =37a(11) =69a(12) =120a(13) =233a(14) =417a(15) =781a(16) =1386a(17) =2561a(18) =4638a(19) =8387a(20) =15495a(21) =27709a(22) =51580a(23) =94054a(24) =176266a(25) =330004a(26) =618846a(27) =1174439a(28) =2216002a(29) =4232301