%I #7 Mar 30 2012 18:39:04
%S 1,2,3,2,5,4,7,4,9,10,1,4,7,4,5,2,3,2,9,10,1,2,3,2,5,4,7,4,9,10,1,4,7,
%T 4,5,2,3,2,9,10,1,2,3,2,5,4,7,4,9,10,1,4,7,4,5,2,3,2,9,10,1,2,3,2,5,4,
%U 7,4,9,10,1,4,7,4,5,2,3,2,9,10,1,2,3,2,5,4,7,4,9,10,1,4,7,4,5,2,3,2,9
%N Least k > 0 such that the last digit of k^n is the same as the last digit of n^k.
%F a(n) is a periodic sequence with period (1, 2, 3, 2, 5, 4, 7, 4, 9, 10, 1, 4, 7, 4, 5, 2, 3, 2, 9, 10, ) of length 20
%o (PARI) a(n)=if(n<0,0,k=1; while(abs(k^n%10n^k%10)>0,s++); s)
%K base,easy,nonn
%O 1,2
%A _Benoit Cloitre_, Aug 13 2002
