  Given a Banach space $A$ and fix a non-zero $\varphi\in A^*$ with
$\|\varphi\|\leq 1$. Then the product $a\cdot b=\langle\varphi, a\rangle\ b$
turning $A$ into a Banach algebra which will be denoted by $_\varphi A.$ Some
of the main properties of $_\varphi A$ such as Arens regularity, $n$-weak
amenability and semi-simplicity are investigated.
