**T**he current puzzle is as follows:

*Define the *symmetric* of an integer as the integer obtained by inverting the order of its digits, eg *4321* is the symmetric of *1234*. What are the numbers for which the square is equal to the symmetric of the square of the symmetric? *

**I** first consulted stackexchange to find a convenient R function to create the symmetric:

int2digit=function(x){
as.numeric(sapply(sequence(nchar(x)),
function(y) substr(x, y, y)))}
digit2int=function(a){
as.numeric(paste(a,collapse=""))}
flip=function(x){
digit2int(rev(int2digit(x)))}

and then found that all integers but the multiples of 10 are symmetric! As can be found on a piece of paper *(but took me more time with my left hand!)*

Filed under: Books, Kids, R Tagged: digits, Le Monde, mathematical puzzle, number theory, R

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