496 (four hundred [and] ninety-six) is the natural number following 495 and preceding 497.
In 1984, Michael Green and John H. Schwarz realized that one of the necessary conditions for a superstring theory to make sense is that the dimension of the gauge group of type I string theory must be 496.
Their discovery started the first superstring revolution.
It was realized in 1985 that the heterotic string can admit another possible gauge group, namely E8 x E8.
The UK's Ofcom reserves telephone numbers in many dialing areas in the 496 local block for fictional purposes, such as 0114 496-1234.