Theta series of square lattice (or number of ways of writing n as a sum of 2 squares). Often denoted by r(n) or r_2(n).
A004018
Theta series of square lattice (or number of ways of writing n as a sum of 2 squares). Often denoted by r(n) or r_2(n).
Terms
- a(0) =1a(1) =4a(2) =4a(3) =0a(4) =4a(5) =8a(6) =0a(7) =0a(8) =4a(9) =4a(10) =8a(11) =0a(12) =0a(13) =8a(14) =0a(15) =0a(16) =4a(17) =8a(18) =4a(19) =0a(20) =8a(21) =0a(22) =0a(23) =0a(24) =0a(25) =12a(26) =8a(27) =0a(28) =0a(29) =8
External references
- oeis: A004018