seven is the one number D for which the equation 2n − D = x2 has more than two remedies for n and x normal. Especially, the equation 2n − 7 = x2 is named the Ramanujan–Nagell equation. Certainly there is also the perfectly-identified Tale of Pharaohs aspiration with regards to the seven Excess fat cows and 7 skinny cows. In brief, the m