a(n) = 7*n-a(n-1)+1 with n>1, a(1)=4. 4, 11, 11, 18, 18, 25, 25, 32, 32, 39, 39, 46, 46, 53, 53, 60, 60, 67, 67, 74, 74, 81, 81
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