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本帖最后由 王守恩 于 2021-3-9 09:20 编辑
你这个通项还真不好找(首位在不断变化,倒过来写好了倒回去又是问题)
\(S=\frac{ 10^n (9 n - 10) + 10}{81}\)
LinearRecurrence[{21, -120, 100}, {0, 10, 210}, 18]
{0, 10, 210, 3210, 43210, 543210, 6543210, 76543210, 876543210,
9876543210, 109876543210, 1209876543210, 13209876543210,
143209876543210, 1543209876543210, 16543209876543210,
176543209876543210, 1876543209876543210, 19876543209876543210,
\(S=\frac{10^n -9 n - 1}{81}\)
LinearRecurrence[{12, -21, 10}, {0, 1, 12}, 18]
{0, 1, 12, 123, 1234, 12345, 123456, 1234567, 12345678,
123456789, 1234567900, 12345679011, 123456790122,
1234567901233, 12345679012344, 123456790123455,
1234567901234566, 12345679012345677, 123456790123456788,
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