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A recursion for the total number of 1's in binary expansions of the first natural numbers?

Let $$a(n)=a(2^k-n)+k(n-2^{k-1})$$ for $$1 \leqslant {2^{k - 1}} < n \leqslant {2^k}$$ with initial values $a(0)=0, a(1)=0, a(2)=1.$ The first values are $0,0,1,2,4,5,7,9,12,13,15,\dots.$ Compari …