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%I #5 Mar 30 2012 18:39:02
%S 2,1,1,2,1,2,1,2,1,1,2,1,2,1,2,1,1,1,2,1,1,2,2,2,1,2,1,2,1,2,1,1,1,2,
%T 1,1,2,1,2,2,2,1,2,1,2,1,1,1,2,1,1,1,2,1,1,1,2,1,1,2,2,2,1,2,1,2,1,1,
%U 2,1,1,2,1,1,1,2,1,1
%N Array A(i,j)= T(prime(i)^j) read by antidiagonals, where T(x) denote the "type" of the integer x: T(m)=1 or 2 depending on whether 1 or 2 is a descendant of n in the Half-totient tree.
%H K. S. Brown, <a href="http://www.mathpages.com/home/kmath168.htm">The Half-Totient Tree</a>
%e Array begins (rows labeled i=1,2,..., columns labeled j=1,2,3,...):
%e 2 2 1 2 1 2 1 2 1 2...
%e 3 1 1 1 1 1 1 1 1 1...
%e 5 2 2 2 2 2 2 2 2 2...
%Y Cf. A023022.
%K easy,nonn,tabl
%O 1,1
%A _Benoit Cloitre_, Jun 03 2002
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