So far I understand:

E = F.d = F.(2.pi.r)*(no. of revolutions) = 2T.pi.n

And

P = E/t = 2T.pi.n/t - but n/t is revolutions per second, so:

P = 2T.pi.f f = rev/second

This is where I'm having trouble, because

1 rev/sec = 60 rpm, so I'd say:

P = 2T.pi.60.N

but in the textbook and online it says P = 2(pi)TN/60 so I'm not sure what's going on...

Anyone know what's going on?