199810domain: NAppears in sequencesE.g.f.: exp(2*arcsin(x)).at n=9A166741Abundant numbers of the form k^2 + 1.at n=5A178458Numbers k with Goldbach partitions (p,q) and (r,s) such that k | (p*q -1) and k | (r*s +1).at n=21A336584