TriangleSum←{
     ⍺←0
     row←⊃⍵
     2≥≢row:(⍺+row)∇ 1↓⍵
     0∊⍴⍵:⍺
     coeffs←1,1,⍨2⍴⍨¯2+≢row
     k←coeffs/⍳≢row
     sums←+⌿↑(⍺⌿⍨2⍴⍨≢⍺)(coeffs/row)
     ⌊/(k{⌊/⍵}⌸sums)∇ 1↓⍵
 }