OFFSET
1,3
FORMULA
a(n) = 2*n-1-A062854(n). - Chai Wah Wu, Oct 13 2023
EXAMPLE
a(4)=4 because there are 7 integer non-products for the 4 X 4 multiplication table (5 7 10 11 13 14 15), which is 4 more than the 3 non-products for the 3 X 3 multiplication table (5 7 8).
PROG
(Python)
from itertools import takewhile
from sympy import divisors
def A062855(n): return (n<<1)-1-sum(1 for i in range(1, n+1) if all(d<=i for d in takewhile(lambda d:d<n, divisors(n*i)))) # Chai Wah Wu, Oct 13 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Ron A. Lalonde (ronronronlalonde(AT)hotmail.com), Jun 25 2001
STATUS
approved