This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
When going to 8 X 8, the added entries 8,16,24 are already known, so a(7)=3: .1..2..3..4..5..6..7....8 * ....4..6..8.10.12.14...16 * .......9.12.15.18.21...24 * .........16.20.24.28...32 ............25.30.35...40 ...............36.42...48 ..................49...56 .......................64
A108407 := proc(n) n+1-A062854(n+1) ; end proc: seq(A108407(n),n=1..40) ; # R. J. Mathar, Oct 02 2020
nmax = 100; A062854 = Table[u = If[n == 1, {}, Union[u, n Range[n]]]; Length[u], {n, 1, nmax+1}] // Differences // Prepend[#, 1]&; a[n_] := n + 1 - A062854[[n+1]]; Table[a[n], {n, 1, nmax}] (* Jean-François Alcover, Oct 02 2020 *)
from itertools import takewhile from sympy import divisors def A108407(n): return n+1-sum(1 for i in range(1,n+2) if all(d<=i for d in takewhile(lambda d:d<=n,divisors((n+1)*i)))) # Chai Wah Wu, Oct 13 2023