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发表于 2009-3-20 22:24:50
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来自 美国
好像一共780个。我的方法比较土,- t = Sort@Join[x = {a, b, c, d}, x, x[[1 ;; -2]]];
- t1 = Fold[Append, t, {1, 1}];
- t2 = Fold[Append, t, {7, 7}];
- lists = Permutations[
- Range[0,
- 9], {4}][[506 ;; -1]];(*Select 4 numbers for a, b,c, and d. a \
- cannot be zero*)
- res1 = Select[
- Map[FromDigits,
- Map[t1 /. # &, Map[Solve[{a, b, c, d} == #][[1]] &, lists]]],
- PrimeQ];
- res2 = Select[
- Map[FromDigits,
- Map[t2 /. # &, Map[Solve[{a, b, c, d} == #][[1]] &, lists]]],
- PrimeQ];
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