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Search: id:A131529
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| A131529 |
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Number of permutations of {1,2,...n} for which differences of adjacent numbers are all distinct. |
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+0
1
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| 1, 2, 4, 12, 44, 176, 788, 3936, 23264, 152112, 1104876, 8725320
(list; graph; listen)
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OFFSET
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1,2
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PROGRAM
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(C++) #include <iostream> #include <vector> #include <set> #include <algorithm> using namespace std; inline int k(const vector<int> & s) { const int n = s.size() ; set<int> diffs ; for(int i=1; i<n; i++) { const int thisdiff = s[i]-s[i-1] ; if ( diffs.find(thisdiff) != diffs.end() ) return 0 ; else diffs.insert(thisdiff) ; } return 1 ; } int main(int argc, char *argv[]) { for(int n=1 ; ; n++) { vector<int> s; for(int i=1; i<=n; i++) s.push_back(i) ; unsigned long long resul=0 ; do { resul += k(s) ; } while( next_permutation(s.begin(), s.end()) ) ; cout << n << " " << resul << endl ; } return 0 ; } - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 25 2007
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CROSSREFS
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Cf. A040018, A091217, A006967.
Sequence in context: A096802 A139669 A039301 this_sequence A074449 A131387 A004527
Adjacent sequences: A131526 A131527 A131528 this_sequence A131530 A131531 A131532
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KEYWORD
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more,nonn
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AUTHOR
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Vladeta Jovovic (vladeta(AT)Eunet.yu), Aug 26 2007
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EXTENSIONS
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2 more terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 25 2007
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