# Permutations Coprime &...
Leroy Quet
qqquet at mindspring.com
Mon Mar 17 02:06:22 CET 2003
I have discussed a less-limiting variation of this problem before
(sans the a(k-1)+a(k+1) coprime to a(k) condition).
For every positive integer n, what are the number of permutations,
a(1),a(2),a(3),...,a(n),
of {1,2,3,...,n}
where GCD(a(k),a(k+1)) = 1 for all k, 1<=k<=n-1;
AND where, as well,
GCD(a(k),a(k-1)+a(k+1)) = 1 for all k, 2<=k<=n-1?
I think the sequence begins:
1, 2, 2, 2,...
Thanks,
Leroy Quet
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