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The smallest Carmichael number that has 4 distinct prime factors (7 * 11 * 13 * 41 = 41041). [Patterson]
41041 is a curious Carmichael number. It happens to be the T(286) = 286th triangular number as well, since 286*(286+1)/2 = 41041. Amazingly, the 41041st triangular number: 41041*(41041+1)/2 = 842202361 = 7 * 11 * 13 * 41 * 20521 is itself a Carmichael number. This was discovered by Jonathan vos Post, who calls numbers such as 842202361 = T(T(286)) "Iterated Triangular Numbers" or "Jonathan Numbers." [Carmichael]
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