Function for artist and singer (7)

I believe the answer is:

sinatra

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'singer' is the definition.
(Frank Sinatra)

'function for artist' is the wordplay.
'function' becomes 'sin' (mathematical function).
'for artist' becomes 'atra' (I can't justify this - if you can you should believe this answer much more).
'sin'+'atra'='SINATRA'

'and' acts as a link.

Can you help me to learn more?

(Other definitions for sinatra that I've seen before include "Francis Albert ..., singer and actor" , "Francis Albert, mourned singer" , "Vocal artist" , "'Ol' Blue Eyes'" , "Was his singing a strain?" .)

I've seen this clue in The Guardian.

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