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n* (n+1) where n is a natural number.

If one cigarette is already lit, we can lit the other one up.

I think it is 88.
1*1+1=2
2*2+2=6
6*3+3=21
21*4+4=88
88*5+5=445
Hence 88 is the missing number

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Hi,
My name is Priyanka. I live in Bangalore. I am new to the forum.:)

I think I require some more info. I need to know what was the room number.