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A114433
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Last digit (the checksum) of 10-digit ISBN numbers, 10 is represented as "X".
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0
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9, 7, 5, 3, 1, 10, 8, 6, 4, 8, 6, 4, 2, 0, 9, 7, 5, 3, 1, 5, 3, 1, 10, 8, 6, 4, 2, 0, 9, 2, 0, 9, 7, 5, 3, 1, 10, 8, 6, 10, 8, 6, 4, 2, 0, 9, 7, 5, 3, 7, 5, 3, 1, 10, 8, 6, 4, 2, 0, 4, 2, 0, 9, 7, 5, 3, 1, 10, 8, 1, 10, 8, 6, 4, 2, 0, 9, 7, 5, 9, 7, 5, 3, 1, 10, 8, 6, 4, 2, 6, 4, 2, 0, 9, 7, 5, 3, 1, 10
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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LINKS
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FORMULA
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The first nine digits of ten-digit ISBN numbers are assigned according to the language, publisher and book. The final digit is a checksum: 1 x the first digit, 2 x the second digit, ... 9 x the ninth digit, reduced modulo 11 and 10 is printed as "X".
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PROG
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(Python)
def a(n): return sum((i+1)*int(s) for i, s in enumerate(str(n).zfill(9)))%11
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CROSSREFS
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KEYWORD
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easy,nonn,base
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AUTHOR
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STATUS
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approved
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