a(n) = 5^n*(5^n-1)/2.A162729a(n) = 5^n*(5^n-1)/2.Terms a(0) =0a(1) =10a(2) =300a(3) =7750a(4) =195000a(5) =4881250a(6) =122062500a(7) =3051718750a(8) =76293750000External referencesoeis: A162729