# 1800 followers problem

Calculus Level 5

$\large \sum_{k=1}^{1800} \psi(k)$

If the above sum can be expressed as $$aH_b-c\gamma-d$$ for some not necessarily distinct positive integers $$a,b,c$$ and $$d$$, evaluate $$a+b+c+d$$ where $$b,c$$ is maximum possible.

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