Crossword Genius

Intelligence calculates pi on a general sequence (9)

Ross

I believe the answer is:

espionage

I'm a little stuck... Click here to teach me more about this clue!

'intelligence' is the definition.
(I know that espionage is a type of spying)

'calculates pi on a general sequence' is the wordplay.
'ESPIONAGE' is hidden in amongst the letters.
However, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for espionage that I've seen before include "agent's job" , "hush-hush work" , "Practice of spying" , "secret work" , "undercover work" .)

I've seen this clue in The Times.
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