$\large ^4 7 \equiv 7^A \pmod{660}$

Find the minimum integer value of $A$ satisfying the equation above.

**
Notation
**
:
$_{ }^{ y }{ x }$
is the tetration function

The answer is 3.

**
This section requires Javascript.
**

You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.

Since $\lambda(660)=20$ and $\lambda(20)=4$ , the Carmichael Lambda , we have $7^{7^{7^7}}=7^{7^{3}}\equiv 7^{\boxed{3}}\pmod{660}$