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A062855
First differences of A062851.
7
0, 1, 2, 4, 4, 7, 6, 10, 11, 13, 10, 17, 12, 19, 20, 23, 16, 26, 18, 29, 29, 31, 22, 37, 33, 37, 38, 42, 28, 47, 30, 48, 47, 49, 49, 58, 36, 55, 56, 63, 40, 66, 42, 67, 68, 67, 46, 78, 66, 77, 74, 80, 52, 85, 78, 89, 83
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
KEYWORD
nonn
AUTHOR
Ron A. Lalonde (ronronronlalonde(AT)hotmail.com), Jun 25 2001
STATUS
approved