Duplicate sequences with error
franktaw at netscape.net
franktaw at netscape.net
Thu Jan 25 01:37:00 CET 2007
It appears that A093551 ("a(n) is the smallest number m such that m+k
is the product of k+1 primes for k=0,1,2,...,n. ") is an erroneous
version of A072875 ("Smallest start for a run of n consecutive numbers
of which the i-th has exactly i prime factors."). A093551(7) is
greater then A072875(8) [the offsets for the sequences differ]. I have
verified that A072875(8) = 19896463921 does satisfy the condition,
which shows that A093551 is incorrect.
A093551 includes a Mathematica program. It looks like this program is
assuming that the kth term in the sequence of consecutive values is
divisible by k; this is not necessarily the case (although it is true
for k <= 4 - looking at A072875, it appears to be true for k = 5 as
well, but I don't see why that should be necessary; it would seem that
values could be congruent to 13 or 17 mod 20 as well).
(The corresponding sequence looking at the number of distinct prime
divisors is A086560, which is quite different; this is not the problem.
Incidently, I think the conjecture in A086560 - that the sequence is
finite - is almost certainly false.)
Franklin T. Adams-Watters
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