siev←{2=+⌿0=(⍳3⌈⍵)∘.|⍳⍵}

   siev 10
0 0 1 1 0 1 0 1 0 0

   {⍵/⍳⍴⍵} siev 10
2 3 5 7

   +/ siev 10
4
   +/ siev 100
25

   +/ siev 1e9
WS FULL
siev[0] siev←{2=+⌿0=(⍳3⌈⍵)∘.|⍳⍵}
                           ∧