a(n) = Sum_{k=1..n} binomial(2*k, k) * sigma_2(k).

Terms

a(0) =2a(1) =32a(2) =232a(3) =1702a(4) =8254a(5) =54454a(6) =226054a(7) =1320004a(8) =5744424a(9) =29762704a(10) =115825408a(11) =683698168a(12) =2451800168a(13) =12480950168a(14) =52811505368a(15) =257779918358a(16) =934525722158