Peter Norvig redid Mark Mayzner’s 1965 study of letter frequency in the English language using Google books data:
My distillation of the Google books data gives us 97,565 distinct words, which were mentioned 743,842,922,321 times (37 million times more than in Mayzner’s 20,000-mention collection).
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Enough of words; let’s get back to Mayzner’s request and look at letter counts. There were 3,563,505,777,820 letters mentioned.
It turns out that Wheel of Fortune is pretty spot on - R, S, T, L, N, E are all in the top ten.