LD50 for the rat taking sodium cyanide is 6440 microgram/kg rat weight

NaCN is 0.53 CN.. thus, for a rat LD50 is 3413 micrograms/kg rat weight.

An LD50 is the amount of substance it takes to kill 50 percent of the animals.

second assumption that the same amount it takes to kill a rat will kill a human

3413 micrograms CN/kg x 130 lb/2.2 lb/kg = 201577 micrograms ~ 202 milligrams

Lets assume the paper below has the same amount of cyanide in apple seeds as in the common Vetch seed. So the cyanide compounds are found at 0.74 micromole/g of vetch seed. The molecular weight of cyanide is 12+14 = 26 so that means 19.2 microgram/g apple seed.

201577 micrograms / (19.2 micrograms CN/g apple seed) = 10504 g apple seeds

10504g/1000g/kg = 10.5 kg apple seeds x 2.2 lb/kg = 23.1 pounds of apple seeds

Of course that assumes you would be able to digest the seeds sufficiently to get the full dose and sufficientlly quickly to reach the required toxic amount before it is removed from your system. And not vomit.

If you assume 5 grams apple seeds per apple that is 2100 apples