A062855 First differences of A062851.

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

Author

Ron A. Lalonde (ronronronlalonde(AT)hotmail.com), Jun 25 2001

Keywords

• nonn

Examples

			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).
		

Crossrefs

Cf. A027424, A062851, A062854, A062856, A062857, A062858, A062859.

Programs

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:dChai Wah Wu, Oct 13 2023

Formula

a(n) = 2*n-1-A062854(n). - Chai Wah Wu, Oct 13 2023