check Armstrong

a!localVariables(
  local!n:tostring(ri!num),
  if(sum( power(a!forEach(
    items: enumerate(len(local!n))+1,
    expression: charat(ri!num,fv!item) ),3)) ==ri!num,"yes it is Armstrong number", "no it is not a Armstrong number"))

Did you try anything yourself? Where did you reach? 
And why don't you use the internet to get answers to such basic problems from sites like stackoverflow or geeksforgeeks?

a!localVariables(
local!a: sum(
power(
tointeger(char(code(ri!num))),
len(ri!num)
)
),
if(
local!a = ri!num,
ri!num & " is an Armstrong Number",
ri!num & " is not an Armstrong Number"
),

)