DigitCount
 Usage
• DigitCount[n, b, d]用来给出n的b进制表示中数字d的个数.
• DigitCount[n, b]用来给出n的b进制表示中数字1，2，...,b-1, 0的个数.
• DigitCount[n]用来给出n的10进制表示中数字1，2，...,9, 0的个数.
Notes
• DigitCount[n]等价于 DigitCount[n, 10, Mod[Range[10],10]].
 Further Examples
Here is a small number.
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Here are two ways to see its digits in base  .
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Out[2]//BaseForm=
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Out[3]=
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This counts how many times  occurs in the base  expansion of x.
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Out[4]=
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In the list of digits there are  ones,  two,  threes,  fours,  fives,  sixes and  zeros.
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Out[5]=
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