a(n) = 7*(10^(2n+1)-1)/9 - 7*10^n.A332170a(n) = 7*(10^(2n+1)-1)/9 - 7*10^n.Terms a(0) =0a(1) =707a(2) =77077a(3) =7770777a(4) =777707777a(5) =77777077777External referencesoeis: A332170