%I #21 Aug 21 2020 12:30:03

%S 5,20,1,15,9,14,19,18,8,12,4,3,21,13,6,16,7,23,25,2,22,11,24,10,17,26

%N a(n) indicates which letter of the English alphabet is the n-th most common.

%C This is according to Mayzner revisited (Peter Norvig), Cornell, British National Corpus and the Brown corpus.

%D Martin Gardner, "Codes, Ciphers, and Secret Writing." Dover Publications, Inc. New York 1984.

%D M. S. Mayzner, Margaret Elizabeth Tresselt, "Tables of Single-letter and Digram Frequency Counts for Various Word-length and Letter-position Combinations," Psychonomic Press, 1965.

%D A. Young," Mathematical Ciphers: From Caesar to RSA." Mathematical World, Volume 25. American Mathematical Society 2006.

%H Cornell, Department of Mathematics, Math Explorer's Club, <a href="http://www.math.cornell.edu/~mec/2003-2004/cryptography/subs/frequencies.html">English Letter Frequency</a>.

%H Gifted Mathematics, Learn How to be Successful in Mathematics Competitions Worldwide, <a href="http://www.giftedmathematics.com/2013/06/the-undecipherable-cipher-middle.html">The Undecipherable Cipher: Middle Secondary Mathematics</a>.

%H Brian Kelk, <a href="http://www.bckelk.ukfsn.org/words/etaoin.html">Some examples of letter frequency rankings in English</a>.

%H Peter Norvig, <a href="http://norvig.com/mayzner.html">English Letter Frequency Counts: Mayzner Revisited or ETAOIN SRHLDCU</a>.

%H Prooffreader.com, <a href="https://web.archive.org/web/20140607165152/http://www.prooffreader.com/2014/05/graphing-distribution-of-english.html">Graphing the distribution of English letters towards the beginning, middle or end of words</a>. [Via Wayback Machine]

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Letter_frequency">Letter frequency</a>.

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Gadsby_(novel)">Gadsby (novel)</a>.

%e The most common letter of the English alphabet is the fifth letter 'E', so a(1)=5; the second most common letter is the twentieth letter 'T', so a(2)=20; the third most common letter is 'A', so a(3)=1; etc.

%t ToCharacterCode["etaoinsrhldcumfpgwybvkxjqz"] - 96

%Y Cf. A005224, A049525, A055508, A126810.

%K fini,full,nonn

%O 1,1

%A Peter Norvig and _Robert G. Wilson v_, Aug 24 2015