[seqfan] A026478 [was A026480)

[Chris Thompson]

On Sep 22 2016, israel at math.ubc.ca wrote:

>A026480: "a(n) = least positive integer > a(n-1) and not a(i)*a(j)*a(k) for 
>1<=i<=j<=k<=n." has Data 1, 2, 4, 5, 6, 7, 9, 11, 13, 15, 17, 19, 21, 23, 
>27, 29, 31, 33, 37, 39, 41, 43, 47, 51, 53, 57, 59, 61, 67, 69.
>
>This doesn't make any sense to me. Since a(1) = 1, any a(n) = 
>a(i)*a(j)*a(k) for the case i=j=1, k=n. Or if you don't allow this, the 
>sequence would be the same as A026478: "a(n) = least positive integer > 
>a(n-1) and not of form a(i)*a(j)*a(k) for 1<=i<=j<=k<n."
>
>What is this sequence supposed to be?

I cannot answer that!

But A026478 itself seems to be in a bit of a mess. The title description
is equivalent to "1, or number of repeated prime factors is 1 mod 3", but
the incorrect comment "Number of repeated prime divisors of n is a square"
has caused some recent "corrections", such as removing 128.

This probably needs to be split into two sequences.

-- 
Chris Thompson
Email: cet1 at cam.ac.uk