Add A000959 / Lucky

It is really slow at the moment, but the logic is very
lightweight. I'm suspecting an issue in rakudo.

lib/Math/Sequences/Integer.pm

@@ -418,7 +418,17 @@ our @A000796 is export = lazy Pi-digits;
 # A000798 / quasi-orders or topologies
 our @A000798 is export = 1, &NOSEQ ... *;
 # A000959 / Lucky
-our @A000959 is export = 1, &NOSEQ ... *;
+# kickstart the sequence manually to make sure we don't rotorize with 0 elems
+my $lucky-iterator = ((1…∞).rotor(1 => 1).flat.rotor(2 => 1).flat).skip(2).iterator;
+our @A000959 is export = 1, 3,
+{
+    my $val = $lucky-iterator.pull-one;
+    $lucky-iterator = Seq.new($lucky-iterator) # rewrap
+                      .rotor(  $val - 1 - 2 - ++$ => 1, # some elems are already behind
+                              ($val - 1           => 1) xx ∞)
+                      .flat.iterator;
+    $val
+} ... *;
 # A000961 / prime powers
 our @A000961 is export = 1, &NOSEQ ... *;
 # A000984 / binomial(2n,n)