65848domain: NAppears in sequencesa(n) is the smallest number of the form k*a(n-1)+a(n-2) for k>0 that is relatively prime to n, with a(0) = 0 and a(1) = 1.at n=21A206241Expansion of Product_{k>=1} ((1 + x^k) / (1 - x^(4*k)))^k.at n=22A285458a(0) = 1; thereafter a(n) = Sum_{k=1..n} (2*k)^k * Stirling1(n,k).at n=5A351274