Answer by Parcly Taxel for Is there any other number that has similar...
This is a very interesting question…$\newcommand{sopfr}{\operatorname{sopfr}}$$f(n)=\frac{n(n+1)}2$ and $g(n)=\sopfr(n)$, the sum of prime factors of $n$ with repeats (OEIS A001414). We want $n$ such...
View ArticleIs there any other number that has similar properties as $21$?
It's my observation.Let$$n=p_1×p_2×p_3×\dots×p_r$$where $p_i$ are prime factors and$f$ and $g$ are the functions$$f(n)=1+2+\dots+n$$And$$g(n)=p_1+p_2+\dots+p_r$$If we put $n=21$...
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