QuoteYou're kidding me when you remember 1/sqrt(2*pi)~ 0.4, e^3~ 20. Don't forget e = 2.71..... as well.There are millions of numbers like this. And we don't need the Ansatz e = 2.71 (kind of cheating, yes?)I don't remember million numbers, about 10 numbers i guess -- Pi, e, sqrt(2), sqrt(3), log(2), log(10), this kind of things. If you traded derivatives or were a derivatives quant, you'd know that 1/sqrt(2*pi)~ 0.4. When you need to calculate Black Scholes approximately in your mind few times, you know. I am not that good with remembering logs, i remember log(2) ~ 0.7. To make sure i remember log(10) i use checksum log(2)+log(10) ~ 3. It's the same equality as the one that i used -- e^3~20, expresses the sum of two most important logs. As i said, there are indeed millions of numbers to remember in your approach with Newton Rapson, i advocate just remembering one or two.