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2↑↑↑↑↑2 = ? (↑ is Knuth's up-arrow)
2↑↑↑↑↑2 = 2↑↑↑↑2 = ... = 2↑2 = 2^2 = 4
Derive the general expression for million, billion... (if the prefix number is n)
10^(3+3n)
The word million comes from the Italian "mille" meaning "thousand", which is definitely weird. But after million, the numbers in the name are consequent natural numbers. Let's take some examples: bi means 2, tri means 3, so let's try to write billion and trillion down:
billion = 1 000 000 000 = 10^9
trillion = 1 000 000 000 000 = 10^12
We have a pattern: 9, 12, 15... It's times 10^3 for every next number. Now if we go back and the other way, we have million = 10^6, thousand = 10^3. Since bi is 2, million is 1, and thousand is 0. Even though its "name" number is 0, thousand is 10^3. That means there's always a constant multiplier of 10^3.
What do squares of numbers of the form 11...1 look like?
Squares of numbers like 11, 1111, etc. give palindromic numbers - numbers that can be read from left to right the same as from right to left:
111*111=12321
Of course, numbers like 111 are also palindromic.
#math #mathematics #numbers #palindrome #square #hartree_math