Ramanujan constant

The Ramanujan Constant is a spectacular almost-integer, equal to $$e^{\pi\sqrt{163}} \approx 262537412640768743.9999999999992500725971981$$.

Ramanujan, ironically, did not coin this number. It was coined by Simon Plouffe, based on an April Fool's joke played on the Scientific American readers by Martin Gardner, where he claimed that $$e^{\pi\sqrt{163}}$$ was actually an integer and that Ramanujan himself hypothesized this.