WOLFRAM|DEMONSTRATIONS PROJECT

Consecutive Smooth Numbers

​
the
th
n
prime
5
(the prime
11
)
index
4
of
36
n
n factored
n+1 factored
2
2
3
3
3
2
2
4
2
2
5
5
5
2×3
generated by Stormer's method with 5
9
5
The smoothness of a number is its maximal prime factor. The number
3×7×11×17×23×83
has smoothness 83,
2
2
4
37
has smoothness 37, and
5×13×29×41×97
has smoothness 97. All three numbers can be considered to be 97-smooth as well, since
97>83
and
97>37
. Multiplied out, these numbers are 7496643, 7496644, and 7496645, making this a consecutive 97-smooth triplet.
For a given prime
n
, all consecutive
n
-smooth pairs can be found via Størmer's method [1]. For this Demonstration, all 97-smooth pairs were found. The number 97 is the
th
25
prime. There are
25
2
=33554432
subsets of these primes. The products of these subsets form the
k
value in the Pell equation
2
x
-2k
2
y
=1
. All of these equations were analyzed, with 21805 prime subsets yielding solutions. For smoothnesses above 97, solutions will be missing.
The largest proven maximal consecutive smooth pair is
3
2
2
23
2
47
83×103×107×139×
2
151
2
173
and
3
3
5×
2
7
13×19×43×59×61×71×89×109×
3
167
[2].