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Task/Left-factorials/D/left-factorials.d

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+import std.stdio, std.bigint, std.range, std.algorithm, std.conv;
+
+BigInt leftFact(in uint n) pure nothrow /*@safe*/ {
+    BigInt result = 0, factorial = 1;
+    foreach (immutable i; 1 .. n + 1) {
+        result += factorial;
+        factorial *= i;
+    }
+    return result;
+}
+
+void main() {
+    writeln("First 11 left factorials:\n", 11.iota.map!leftFact);
+    writefln("\n20 through 110 (inclusive) by tens:\n%(%s\n%)",
+             iota(20, 111, 10).map!leftFact);
+    writefln("\nDigits in 1,000 through 10,000 by thousands:\n%s",
+             iota(1_000, 10_001, 1_000).map!(i => i.leftFact.text.length));
+}