Number of arrangements of 4 numbers x(i) in -n..n with the sum of x(i)*x(i+1) equal to zero.

Terms

a(0) =29a(1) =117a(2) =257a(3) =497a(4) =749a(5) =1205a(6) =1569a(7) =2161a(8) =2765a(9) =3589a(10) =4177a(11) =5377a(12) =6077a(13) =7253a(14) =8561a(15) =10017a(16) =10941a(17) =12837a(18) =13873a(19) =16017a(20) =17933a(21) =19845a(22) =21105a(23) =24097a(24) =25981a(25) =28245a(26) =30593a(27) =33729a(28) =35325a(29) =39397