Consecutive identical values of omega
franktaw at netscape.net
franktaw at netscape.net
Sun Jan 29 08:21:08 CET 2006
I have been looking at the question of how many consective integers
there are with omega (the number of distinct prime factors) equal to n.
Trivially, for n = 0 the maximum is 1 (for 1), and for n=1, I think
current results are sufficient to show the maximum is 4 (2 - 5).
Checking up to 10^11, the maximum for n=2 is 8 (141 - 148, and again
212 - 219); this is probably the maximum. For n=3, the maximum in this
range is 15 (found 3 times: 17233173 - 17233187, 28926285 - 28926299,
and 83590082 - 83590096). I don't have much confidence that this is
actually the limit. For n=4, I didn't even bother looking.
Perhaps somebody with a faster machine and a better factorization
program (I used PARI) can extend these results.
Actual upper bounds are much higher. The best easily provable upper
bound is p_{n+1}# - 1 (the product of the first n+1 primes, minus 1).
This is 29 for n=2, 209 for n=3. It seems very unlikely that the value
for n=2 is greater than 9, since any sequence of 10 consecutive
integers must contain both a multiple of 6 and a multiple of 10;
getting the cofactors of each to be limited to the prime divisors
thereof seems very unlikely.
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