OFFSET
1,3
COMMENTS
Number of distinct products i*j for 2<=i<=j<=n. - Chai Wah Wu, Oct 14 2023
EXAMPLE
There are a(7) = 20 distinct composite numbers in the 7x7 multiplication table:
1 2 3 4 5 6 7
4* 6* 8* 10* 12 14*
9* 12* 15* 18* 21*
16* 20* 24* 28*
25* 30* 35*
36* 42*
49*
MAPLE
A334454 := proc(n)
local dcom, i, j;
dcom := {} ;
for i from 1 to n do
for j from 1 to i do
if not isprime(i*j) and i*j> 1 then
dcom := dcom union {i*j} ;
end if;
end do:
end do:
print(n, dcom) ;
nops(dcom) ;
end proc:
seq(A334454(n), n=1..70) ; # R. J. Mathar, Oct 02 2020
PROG
(Python)
def A334454(n): return len({i*j for i in range(2, n+1) for j in range(2, i+1)}) # Chai Wah Wu, Oct 14 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Charles Kusniec, Sep 08 2020
STATUS
approved