81683domain: NAppears in sequencesa(n) = (a(n-1) - a(n-3))*7^((1+(-1)^n)/2) with a(6)=5, a(7)=4, a(8)=22.at n=14A215139Expansion of Product_{k>=1} 1/((1 - x^k)*(1 - x^(4*k))).at n=39A318027Numbers k such that k and k+1 have the same sum of powerful divisors (A183097) and this sum is larger than 1.at n=22A349063