Time for an 2014 update…

Task/Digital-root/AWK/digital-root.awk

@@ -0,0 +1,25 @@
+# syntax: GAWK -f DIGITAL_ROOT.AWK
+BEGIN {
+    n = split("627615,39390,588225,393900588225,10,199",arr,",")
+    for (i=1; i<=n; i++) {
+      dr = digitalroot(arr[i],10)
+      printf("%12.0f has additive persistence %d and digital root of %d\n",arr[i],p,dr)
+    }
+    exit(0)
+}
+function digitalroot(n,b) {
+    p = 0 # global
+    while (n >= b) {
+      p++
+      n = digitsum(n,b)
+    }
+    return(n)
+}
+function digitsum(n,b,  q,s) {
+    while (n != 0) {
+      q = int(n / b)
+      s += n - q * b
+      n = q
+    }
+    return(s)
+}