a(n) = { my (b = binary(n)); fromdigits(vector(#b, k, sum(i = 1, ceil(k/2), b[i] * b[k+1-i])) %2, 2); } { b = vector(2^13-1); for (n = 1, #b, b[a(n)] = n; ); print ("0 0"); for (n = 1, #b, print (n " " b[n]); ); } quit