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

1,3

Links

Table of n, a(n) for n=1..57.

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

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

Sequence in context: A164719 A104510 A082515 * A274593 A103622 A328853

Adjacent sequences: A062852 A062853 A062854 * A062856 A062857 A062858

Keyword

nonn

Author

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

Status

approved