This should work…

It seems very inefficient, though

p11/p11.org

@@ -0,0 +1,37 @@
+#+title: Solution for p11
+
+#+begin_src emacs-lisp
+  (setq data '(0 27 5409930 828979 4471 3 68524 170))
+#+end_src
+
+#+RESULTS:
+| 0 | 27 | 5409930 | 828979 | 4471 | 3 | 68524 | 170 |
+
+Define the auxiliary functions
+#+begin_src emacs-lisp
+  (defun number-digits (x)
+    (1+ (floor (log x 10))))
+
+  (defun split (x)
+    (let ((n (number-digits x)))
+      (--map (funcall it x (expt 10 (/ n 2))) '(/ %))))
+
+  (defun blink (x)
+    (cond
+     ((eq x 0) '(1))
+     ((eq (% (number-digits x) 2) 0) (split x))
+     (t (list (* 2024 x)))))
+ #+end_src
+
+ #+RESULTS:
+ : blink
+
+And now compute
+ #+begin_src emacs-lisp
+   (length (-last-item  (--iterate (-mapcat #'blink it) data (1+ 75))))
+ #+end_src
+
+ #+RESULTS:
+ : 194482
+
+(-mapcat #'blink data)