a(n) = (25^n - 1)/24.A218728a(n) = (25^n - 1)/24.Terms a(0) =0a(1) =1a(2) =26a(3) =651a(4) =16276a(5) =406901a(6) =10172526a(7) =254313151a(8) =6357828776a(9) =158945719401External referencesoeis: A218728