(Common LISP)

(defun subsets (k xs)
  (cond ((null xs) 'nil)
	((= 1 k) (loop for x in xs collect (list x)))
	(t (union (subsets k (cdr xs))
		  (mapcar (lambda (x) (cons (car xs) x))
			  (subsets (1- k) (cdr xs)))))))

(defun new-degree-sequence (ds is)
  (let ((ys (copy-list ds)))
    (dolist (i is) (decf (nth i ys)))
    (delete 0 (sort ys #'<))))

(let ((table (make-hash-table :test #'equal)))
  (defun graph-count (ds)
    (cond
      ((equal ds '(1 1)) 1)
      ((< (length ds) 3) 0)
      ((oddp (reduce #'+ ds)) 0)
      (t (or (gethash ds table)
	     (setf (gethash ds table)
		   (reduce #'+
			   (mapcar (lambda (x) (graph-count (new-degree-sequence (cdr ds) x)))
				   (subsets (car ds) (loop for i from 0 below (1- (length ds))
							collect i))))))))))

(defun regular-graph (n k)
  (loop repeat k collect n))


(loop for i from 7 to 20 do
  (format t "~d~%" (graph-count (regular-graph 6 i))))