# Taylor Expansion of Normal CDF

I read the following paragraph which claims to be the Taylor expansion of standard normal CDF for positive $x$.

$1 - \frac{1}{\sqrt{2\pi}}e^{-\frac{x^2}{2}} (a_1k + a_2k^2 + a_3k^3 + a_4k^4 + a_5k^5)$,

where $k:=\frac{1}{1+0.2316419x}, a_1=0.319381530, a_2=-0.356563782, a_3=1.781477937, a_4=-1.821255978, a_5=1.330274429.$

I do not get how this is derived even though I am numerically convinced of its truth. Could anyone explain this to me, please?