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Calculator

For the Euclidean Algorithm, Extended Euclidean Algorithm and multiplicative inverse.

Before you use this calculator

If you're used to a different notation, the output of the calculator might confuse you at first.
Even though this is basically the same as the notation you expect. If that happens, don't panic.
Just make sure to have a look the following pages first and then it will all make sense:

Euclidean Algorithm
For the basics and the table notation
Extended Euclidean Algorithm
Unless you only want to use this calculator for the basic Euclidean Algorithm.
Modular multiplicative inverse
in case you are interested in calculating the modular multiplicative inverse of a number modulo n
using the Extended Euclidean Algorithm

Input

Algorithm

Choose which algorithm you would like to use.

Numbers

Enter the input numbers. Note that you need to enter n before b.
E.g. if you want to know the multiplicative inverse of 26 mod 11, then use n=11 and b=26.

Output

Note: 870 mod 257 ≡ 99, so you could also use this calculator with n=257 and b=99. In that case the table will have less rows, even though it has the same multiplicative inverse.

This is the calculation for finding the multiplicative inverse of 870 mod 257 using the Extended Euclidean Algorithm:

n	b	q	r	t1	t2	t3
257	870	0	257	0	1	0
870	257	3	99	1	0	1
257	99	2	59	0	1	-2
99	59	1	40	1	-2	3
59	40	1	19	-2	3	-5
40	19	2	2	3	-5	13
19	2	9	1	-5	13	-122
2	1	2	0	13	-122	257

Answer

So t = -122. Now we still have to apply mod n to that number:
-122 mod 257 ≡ 135
So the multiplicative inverse of 870 modulo 257 is 135.

Verification

Let i be the answer we just found, so i=135. We also have b=870 and n=257.
If our answer is correct, then i × b (mod n) ≡ 1 (mod n).
Let's see if that's indeed the case.
i × b (mod n) ≡
135 × 870 (mod 257) ≡
117450 (mod 257) ≡
1 (mod 257)

As you can see, i × b (mod n) ≡ 1 (mod n), so our calculation is correct!