I believe your issue is because of the following code:

while (temp > 1) {
	while (temp%div == 0)
		temp = temp/div;
	a.push_back(div);
	div++;
}

Since temp can be very big, and also not have any divisors, you could end up pushing almost 10⁹ numbers into a. This would happen if temp is a large prime, like 999999937.

Also, just in case you don't know, Div1A and Div2A are of different difficulties. Div1A is equivalent to Div2C, so if you're just starting out, try some Div2A problems first.

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