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%I #19 Mar 08 2015 18:24:16
%S 1,2,4,12,44,176,788,3936,23264,152112,1104876,8725320,74715908,
%T 687915040,6782261964,71294227456,796138700016,9409401651840,
%U 117378774461812
%N Number of permutations of {1,2,...n} for which differences of adjacent numbers are all distinct.
%H Joerg Arndt, <a href="/A131529/a131529.txt">lexicopraphically first permutation</a> with distinct differences for n=1..30 (permutations of {0,1,2,..,n-1}, i.e., zero based).
%o (C++) /* gcc -O2 -Wall -lstdc++ A131529.cc */
%o #include <iostream>
%o #include <vector>
%o #include <set>
%o #include <algorithm>
%o using namespace std;
%o inline int k(const vector<int> & s)
%o {
%o const int n = s.size();
%o set<int> diffs;
%o for (int i=1; i<n; i++)
%o {
%o const int thisdiff = s[i]-s[i-1];
%o if ( diffs.find(thisdiff) != diffs.end() ) return 0;
%o diffs.insert(thisdiff);
%o }
%o return 1;
%o }
%o int main(int argc, char *argv[])
%o {
%o for(int n=1; ; n++)
%o {
%o vector<int> s;
%o for(int i=1; i<=n; i++) s.push_back(i);
%o unsigned long long resul=0;
%o do { resul += k(s); }
%o while ( next_permutation(s.begin(), s.end()) );
%o cout << n << " " << resul << endl;
%o }
%o return 0;
%o }
%o /* _R. J. Mathar_, Oct 25 2007 */
%Y Cf. A040018, A091217, A006967.
%K more,nonn
%O 1,2
%A _Vladeta Jovovic_, Aug 26 2007
%E 2 more terms from _R. J. Mathar_, Oct 25 2007
%E 7 more terms from _R. H. Hardin_, Nov 26 2009
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