Search: id:A102381 Results 1-1 of 1 results found. %I A102381 %S A102381 1,2,6,8,60,24,504,576,6480,5760,242352,93312,6200064,5612544,95294880, %T A102381 136249344,13687492608,5022425088,693149184000,472559616000, %U A102381 18501259714560,23441203298304,4435759798272000,1568692666368000 %N A102381 Number of permutations of 1..n in which every pair of adjacent numbers as well as the first and the last entries are relatively prime. %C A102381 a(n)=n*A086595(n). %H A102381 Leroy Quet, Home Page (listed in lieu of email address) %e A102381 a(4)=8 because we have 1234, 1432, 2143, 2341, 3214, 3412, 4123 and 4321. %p A102381 with(combinat): for n from 1 to 7 do P:=permute(n): ct:=0: for j from 1 to n! do if add(gcd(P[j][i+1],P[j][i]),i=1..n-1)=n-1 and gcd(P[j][1], P[j][n])=1 then ct:=ct+1 else ct:=ct fi od: a[n]:=ct: od: seq(a[n], n=1..7); %Y A102381 Cf. A086595, A076220. %Y A102381 Sequence in context: A098239 A140257 A053938 this_sequence A075998 A007849 A100621 %Y A102381 Adjacent sequences: A102378 A102379 A102380 this_sequence A102382 A102383 A102384 %K A102381 nonn %O A102381 1,2 %A A102381 Emeric Deutsch (in collaboration with R. Chandler, V. Jovovic, L. Quet, Z. Seidov and J. Zucker) (deutsch(AT)duke.poly.edu), Apr 09 2005 %E A102381 a(15)=95294880 and a(16)=136249344 from Ray Chandler (rayjchandler(AT)sbcglobal.net) and Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), Apr 12 2005 %E A102381 Many more terms from Max Alekseyev (maxale(AT)gmail.com), Jun 13 2005 Search completed in 0.001 seconds