It is my understanding that double an exponent results in an LL test taking approximately four times longer.

From the

CPU credit calculator, the 49th known Mersenne prime, M74,207,281, takes around 205 GHz-days. The first Mersenne number of prime index with 100 million digits, M332,192,831, needs around 4,941 GHz-days. This also seems reasonable. M601,248,421, the largest Mersenne number with an LL test to date, requires about 16,584 GHz-days, which closely matches the credit that Never Odd or Even received.

However, the numbers become weird after that: the calculator says the first Mersenne number with more than a billion digits, M3,321,928,097, requires just 91,630 GHz-days. The actual value should also be much higher; (3,321,928,097 / 601,248,421)

^{2} ≈ 30.5, and multiplying that by 16,584 gives over 500,000 GHz-days.

So does the time complexity for LL tests stop exhibiting quadratic growth after a certain point? Or is there an error in the calculator?