problem
Xiaolan uses a seven-segment digital tube to represent a special kind of text.
The figure above shows an illustration of a seven-segment digital tube. There are 7 LEDs in the digital tube that can emit light, which are marked as a, b, c, d, e, f, g.
Xiaolan chooses a part of the diode (at least one) to emit light to express characters.
When designing the expression of characters, all light-emitting diodes are required to be connected in one piece.
For example: b is luminous, other diodes are not luminous and can be used to express a kind of character.
For example: c light-emitting, other diodes not light-emitting can be used to express a character.
This scheme and the scheme on the previous line can be used to represent different characters, although they look similar.
For example: a, b, c, d, e glow, f, g not glow can be used to express a character.
For example: b, f are luminous, and other diodes cannot be used to express a character if they don’t, because the luminous diodes are not connected in one piece.
Excuse me, how many different characters can Xiaolan express with a seven-segment digital tube?
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Ideas
This question, as a fill-in-the-blank question, can be done directly, sometimes it is a good way
to count directly. This can count the number of luminous:
1: 7 types
2: 10 types
3: 16 types
4: 20 types
5: 19 types
6: 7 types
7: 1 type
ans = 7 + 10 + 16 + 20 + 19 + 7 + 1 = 80, a
total of 80 types