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A137233
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Number of n-digit even numbers.
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5
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5, 45, 450, 4500, 45000, 450000, 4500000, 45000000, 450000000, 4500000000, 45000000000, 450000000000, 4500000000000, 45000000000000, 450000000000000, 4500000000000000, 45000000000000000, 450000000000000000
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refs;
listen;
history;
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internal format)
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OFFSET
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1,1
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COMMENTS
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a(n) is also the total number of double rows identified numbers in n digit.
For example:
n = 1: 01 23 45 67 89 = 5 double rows;
n = 2: 1011 1213 1415 1617 1819...9899 = 45 double rows;
n = 3: 100101 102103 104105...998999 = 450 double rows;
...
The number of double rows is also A030656. (End)
a(n) is also the number of n-digit integers with an even number of even digits (A356929); a(5) = 45000 is the answer to the question 2 of the Olympiade Mathématique Belge in 2004 (link). - Bernard Schott, Sep 06 2022
a(n) is also the number of n-digit integers with an odd number of odd digits (A054684). - Bernard Schott, Nov 07 2022
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LINKS
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FORMULA
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EXAMPLE
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a(2) = 45 because there are 45 2-digit even numbers.
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PROG
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(Python)
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CROSSREFS
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Cf. A002275, A090843, A097166, A099914, A099915, A037487, A000422, A057138, A014925, A014923, A016313, A002276, A011577, A019518, A053052.
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KEYWORD
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easy,nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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