Here's a definition from Wolfram math world that includes an addition operation for any valid value of k: https://mathworld.wolfram.com/SomosSequence.html https

Here's a definition from Wolfram math world that includes an addition operation for any valid value of k: https://mathworld.wolfram.com/SomosSequence.html https://mathworld.wolfram.com/SomosSequence.html Are you talking about the behavior of the floor operator in determining the number of terms in the sum? For k in {1,2,3}, floor(k/2) = 1. So there would only be one term and thus no addition.