The reason BigInt was there was to allow for calculations of 1000! or larger (which was the original intent). However, I don't see how this alone could explain the timing differences. For example, in my original code, the recursive function

• Created one new BigInt
• Compared two BigInts
• Multiplied two BigInts
• Subtracted 2 BigInts

The non-recursive function

• Created 2 BigInts
• Multiplied 2 BigInts

In other words, are you saying that memory allocation for one extra BigInt is that slow??