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%I #3 Mar 23 2015 07:03:54
%S 1,2,3,0,21,22,23,20,31,32,33,30,1,2,3,0,211,212,213,210,221,222,223,
%T 220,231,232,233,230,201,202,203,200,311,312,313,310,321,322,323,320,
%U 331,332,333,330,301,302,303,300,11,12,13,10,21,22,23,20,31,32
%N Apply the transformation 0 -> 1 -> 2 -> 3 -> 0 to the digits of n written in base 4; do not convert back to base 10.
%C Base 4 variant of A256078 (base 2) and A048379 (base 10). See A256303 - A256308 for bases 3 through 8, A256289 for base 9, and A256294 for the variant where the result is converted back to base 10.
%e a(4) = 21 because 4 = "10" (in base 4) becomes "21".
%e a(15) = 0 because 15 = "33" (in base 4) becomes "00".
%o (PARI) A256304(n,b=4)=!n+eval(Strchr(apply(d->(d+1)%b+48, digits(n,b))))
%K nonn,base,easy
%O 0,2
%A _M. F. Hasler_, Mar 22 2015