You are right. What I remembered before is an approximation used in a program.
I just got a table from web:
MIDI Note Number to Frequency Conversion Chart
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MIDI MIDI MIDI
Note Frequency Note Frequency Note Frequency
C 0 8.1757989156 12 16.3515978313 24 32.7031956626
Db 1 8.6619572180 13 17.3239144361 25 34.6478288721
D 2 9.1770239974 14