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ROSECODE 435

Harmonic variations

Philippe_57721 · Programming ·

It is well known that the Harmonic serie n11n is divergent.

A more surprising result is that if we remove all numbers containing at least one digit 9 the corresponding serie is convergent.

What is nS1,2,1,41n

where S1,2,1,4 is the set of all numbers with exactly one digit 2 and one digit 4 in their base-10 representation

S1,2,1,4={24,42,124,142,204,214,234,240,241,243,245}

Answer format: Give the result with the first 20 digits after the decimal point.

[My timing : < 1 sec]