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A362443
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Numbers k with property that the set of letters in the English name for k does not contain two letters that are adjacent in the alphabet.
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0
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0, 2, 3, 4, 6, 7, 9, 10, 11, 19, 20, 23, 29, 40, 42, 50, 52, 90, 99
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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COMMENTS
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In other words, k such that row k of the triangle A073029, when converted to a set, does not contain two consecutive numbers.
Since hundred, thousand, million, all contain two consecutive letters, there are no other terms.
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REFERENCES
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GCHQ, The GCHQ Puzzle Book, Penguin, 2016. See pages 99 and 286.
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LINKS
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EXAMPLE
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3 is a term because the set {20, 8, 18, 5} (from t,h,r,e,e) does not contain two consecutive numbers.
But 5 is not a term, since e and f are adjacent in the alphabet.
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PROG
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(Python)
from num2words import num2words as n2w
def ok(n):
w = sorted(c for c in set(n2w(n).replace(" and", "")) if c.isalpha())
return min(ord(w[i+1])-ord(w[i]) for i in range(len(w)-1)) > 1
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CROSSREFS
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KEYWORD
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nonn,word,fini,full
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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