The one liner below seems to work, but time- and space-wise it is slightly inferior to RE Boss's cAO. Though, in my opinion, it is more direct.
NB. word wrap problem
C =: 4 : '(,~x)$(/:@;@( [: </. i.)@,~x){;<@(%&(1+x-~#y))@((1+x-~#y)+/\])/.(*"0
1 |.) y'
ts '276 cAO i.600'
0.226437 1.16933e7
ts '276 C i.600'
0.378538 1.198e7
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