[seqfan] Composites in the i*j multplication table A333996

Richard J. Mathar mathar at mpia-hd.mpg.de
Fri Oct 2 12:51:09 CEST 2020


Does someone understand the a(4)=7 in the A333996(4) count
for composites in the 4x4 multiplication table?
I get a(4)=6, that is the cardinality of {4,6,8,9,12,16},
and a sequence like 0, 1, 3, 6, 10, 14, 20, 25, 31, 37...
See also A027424 (cardinality of the set of all i*j) and A000720
(number of primes in the multiplication table).


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