a(n) = 7*(10^(2n+1)-1)/9 - 6*10^n.A332171a(n) = 7*(10^(2n+1)-1)/9 - 6*10^n.Terms a(0) =1a(1) =717a(2) =77177a(3) =7771777a(4) =777717777a(5) =77777177777External referencesoeis: A332171