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Big Factorial for the HP-42S

Adapted to the HP-42S by Richard Garner

This program calculates approximations for big factorials (N! for N > 253) on the HP-42S. This program was originally written for the 41C and published in the PPC Journal.

Usage:

Enter a non-negative integer and run BN!. The result is returned in Y (the mantissa) and X (the exponent) and is also shown in the alpha register.

Example:


Technical notes:

• For N < 254 the built-in N! function is called.
  
• The precision of the approximation goes down for very large N. All seven digits of the multiplier are correct for N<10 000, for N = 100 000 five digits are correct and for N = 1 000 000 three digits are correct.

Binary files for emulators:
Raw binary: bigfact.raw  Binary for HP-42X: bigfact.42x

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