Ku godt bruge lidt forklaring. Der er også mere elegante måder at få summen end at skulle have den forbi en dataframe.
Let d(n) be the sum of divisors of n (nunbers less than n)
If d(a) = b and d(b) = a, where a is not equal to b, a and b are amicable. Find the sum of amicable numbers under 10000.
a <- c(1:10000)
library(numbers)
b <- unlist(lapply(a, function(x) sum(divisors(x)[1:(length(divisors(x))-1)])))
c <- unlist(lapply(b, function(x) sum(divisors(x)[1:(length(divisors(x))-1)])))
d <- data.frame(opr=a, summen=b, anden = c)
e <- d[which(d$opr==d$anden),]
e <- e[which(e$opr != e$summen),]
sum(e$opr)