7 is the one amount D for which the equation 2n − D = x2 has much more than two remedies for n and x all-natural. Particularly, the equation 2n − 7 = x2 is named the Ramanujan–Nagell equation. Not Every person thinks that cats have nine lives. In some aspects of Spain, Germany, and Iran, it’s claimed that cats have just 7 life! I ponder