Average number of times a coin toss, face up to appear twice in a row?

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Similar problems, draw dice how many times can appear three times in a row is 6:

answer:

1 / p + 1 / (p * p) + 1 / (p * p * p) = 6 + 36 + 216 = 258 times

 

The derivation process:

https://zhuanlan.zhihu.com/p/68358814