Ec primes are primes formed by concatenation in base ten of two consecutive Mersenne numbers, $40952047$, for example.
Some exponents leading to an ec prime are: $51456$, $541456$, $331259$ and $92020$.
It is easy to see that $331259=541456+13-210210$ and $92020=331259-239239$.
Now $92020\equiv -25\pmod {449}$
$541456 +13\equiv -25\pmod {449\cdot 201}$
$210210\equiv 78\equiv -239239 \pmod {449}$
$51456$ is a multiple of $201$.
Is it possible that all this has some explanation?