a(n) = 2*(10^(2n+1)-1)/9 + 5*10^n.A332127a(n) = 2*(10^(2n+1)-1)/9 + 5*10^n.Terms a(0) =7a(1) =272a(2) =22722a(3) =2227222a(4) =222272222a(5) =22222722222External referencesoeis: A332127