I guess the English formula should be fixed with s/ multiplied\K for n-1/ by a-1/, i.e. 
3^3 = 1 + (3 - 1) * (3^0 + 3^1 + 3^2) = 1 + 2 * (1 + 3 + 9) = 1 + 2 * 
+13 = 1 + 26 = 27

[download]
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re^2: [OT] math fulguration by choroba
in thread [OT] math fulguration by Discipulus

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