Uncle Albert says the answer to his maths problem (3465222) is "a prime number of the Zeeman series". This is a fictional series, first used in Flash Gordon by Dr Zarkov who says: "A-ha! I thought it was one of the prime numbers of the Zeeman series."
Despite taking place in circa 1917, the children sing "Happy Birthday to You", which wasn't written until 1924, and didn't game popularity until around 1930.