The next number would be 270₈. The given number has an digit expansion of
267₈ = 2•8² + 6•8¹ + 7•8⁰
If x is the next number, then adding 1 to the both sides gives
x = 2•8² + 6•8¹ + 7•8⁰ + 1
x = 2•8² + 6•8¹ + 7•8⁰ + 1•8⁰
x = 2•8² + 6•8¹ + 8•8⁰
x = 2•8² + 6•8¹ + 1•8¹
x = 2•8² + 7•8¹
x = 2•8² + 7•8¹ + 0•8⁰
and so x = 270₈.
