a(n) = [x^n] Product_{k>=1} (1 + n^2*x^k).

Terms

a(0) =1a(1) =1a(2) =4a(3) =90a(4) =272a(5) =1275a(6) =49284a(7) =124901a(8) =536640a(9) =1620648a(10) =104040100a(11) =223290012a(12) =880969104a(13) =2485978170a(14) =7454471332a(15) =592164776475