Sum {0<=k<=n, k mod 4} (Partial sums of A010873). 0, 1, 3, 6, 6, 7, 9, 12, 12, 13, 15, 18, 18, 19, 21, 24, 24, 25, 27, 30, 30, 31, 33, 36, 36
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