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What a winning combination?

The computer chose a secret code (sequence of 4 digits from 1 to 6). Your goal is to find that code. Black circles indicate the number of hits on the right spot. White circles indicate the number of hits on the wrong spot.

Correct answers: 71

The first user who solved this task is Djordje Timotijevic.

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One man said to the other...

One man said to the other, "You know, there are really only three kinds of people in the world: those who can count, and those who can't.

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Crystal rectifier

In 1874, a paper by Ferdinand Braun (1850-1918) was published in the Annalen der Physik und Chemie describing his discovery of the electrical rectifier effect. He observed that certain crystals of metal sulphides have a larger or smaller resistance to an electric current, depending on its direction of flow. He used a galena crystal, a semiconductor material composed of lead sulfide. He found the rectifying effect especially true if at least one of the electrodes was a pointed wire. Thus, he had discovered the point-contact rectifier effect, the first semiconductor device. This effect wasn't used until over 30 years later in the form of the “cat's whisker”crystal radio detector which ultimately led to the point-contact transistor first produced in 1948.

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