In org-mode:
#+BEGIN_SRC calc :var x=5 :var y=2 2+a*x**y #+END_SRC returns
No org-babel-execute function for calc! How do I enable calc for org-babel-execute?
As described in org documentation:
By default, only 'emacs-lisp' is enabled for evaluation. To enable or disable other languages, customize the 'org-babel-load-languages' variable either through the Emacs customization interface, or by adding code to the init file as shown next:
In this example, evaluation is disabled for 'emacs-lisp', and enabled for `R'.
(org-babel-do-load-languages 'org-babel-load-languages '((emacs-lisp . nil) (R . t)))
So here you could do the following:
(org-babel-do-load-languages 'org-babel-load-languages '((calc . t))) To add to JeanPierre's answer, you can run M-x customize-variable with org-babel-load-languages to modify the list from Emacs.