TeaScript, 18 bytes

x%2Ωr(x--)ßl-x/2)

Pretty simple. The special characters are actually just "abbreviations" for longer code sequences.

I still haven't made permalinks so you'll have to copy paste into the interpreter

Explanation

x%2 &&    // If x is NOT even return falsy, else...
r(x--)    // Range 0-input. Subtracts one from input
m(#       // Loop through range
  l-      // Current item in loop, minus...
    x/2   // input - 1, divided by two
)

TeaScript, 16 bytes 18

x%2Þr(xØ)ßl-x/2)

Pretty simple. The special characters are actually just "abbreviations" for longer code sequences.

I still haven't made permalinks so you'll have to copy paste into the interpreter

Explanation

x%2 &&    // If x is NOT even return falsy, else...
r(x--)    // Range 0-input. Subtracts one from input
m(#       // Loop through range
  l-      // Current item in loop, minus...
    x/2   // input - 1, divided by two
)

_{This answer is non-competing}

TeaScript, 17 bytes

x%2Ωr(x--)ßl-x/2)

Pretty simple. The special characters are actually just "abbreviations" for longer code sequences.

I still haven't made permalinks so you'll have to copy paste into the interpreter

Explanation

x%2 &&    // If x is NOT even return falsy, else...
r(x--)    // Range 0-input. Subtracts one from input
m(#       // Loop through range
  l-      // Current item in loop, minus...
    x/2   // input - 1, divided by two
)

TeaScript, 18 bytes

x%2Ωr(x--)ßl-x/2)

Pretty simple. The special characters are actually just "abbreviations" for longer code sequences.

I still haven't made permalinks so you'll have to copy paste into the interpreter

Explanation

x%2 &&    // If x is NOT even return falsy, else...
r(x--)    // Range 0-input. Subtracts one from input
m(#       // Loop through range
  l-      // Current item in loop, minus...
    x/2   // input - 1, divided by two
)

TeaScript, 17 bytes

x%2Ωr(x--)ßl-x/2)

Pretty simple. I still haven't made permalinks so you'll have to copy paste into the interpreter

Explanation

x%2 &&    // If x is NOT even return falsy, else...
r(x--)    // Range 0-input. Subtracts one from input
m(#       // Loop through range
  l-      // Current item in loop, minus...
    x/2   // input - 1, divided by two
)

TeaScript, 17 bytes

x%2Ωr(x--)ßl-x/2)

Pretty simple. The special characters are actually just "abbreviations" for longer code sequences.

I still haven't made permalinks so you'll have to copy paste into the interpreter

Explanation

x%2 &&    // If x is NOT even return falsy, else...
r(x--)    // Range 0-input. Subtracts one from input
m(#       // Loop through range
  l-      // Current item in loop, minus...
    x/2   // input - 1, divided by two
)