Data update

Task/Digital-root-Multiplicative-digital-root/R/digital-root-multiplicative-digital-root.r

@@ -0,0 +1,36 @@
+numdigits <- function(n) ifelse(log10(n)%%1==0,
+                                1+log10(n),
+                                ceiling(log10(n)))
+
+digmul <- function(n){
+  k <- numdigits(n)
+  get_digit <- function(m) (n%/%10^m)%%10
+  prod(sapply(0:(k-1), get_digit))
+}
+
+mdr_mp <- function(n){
+  m <- n
+  i <- 0
+  while(m > 9){
+    m <- digmul(m)
+    i <- i+1
+  }
+  c("MDR"=m, "MP"=i)
+}
+
+test_nums <- c(123321, 7739, 893, 899998)
+rbind("n"=test_nums, sapply(test_nums, mdr_mp)) |> t()
+
+first5mdr <- function(n){
+  m <- 0
+  nums <- numeric(0)
+  while(length(nums) < 5){
+    if(mdr_mp(m)[1] == n){
+      nums <- c(nums, m)
+    }
+    m <- m+1
+  }
+  setNames(nums, paste0("n_", 1:5))
+}
+
+rbind("MDR"=0:9, sapply(0:9, first5mdr)) |> t()