This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A062855 #5 Oct 14 2023 00:04:32 %S A062855 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, %T A062855 37,38,42,28,47,30,48,47,49,49,58,36,55,56,63,40,66,42,67,68,67,46,78, %U A062855 66,77,74,80,52,85,78,89,83 %N A062855 First differences of A062851. %F A062855 a(n) = 2*n-1-A062854(n). - _Chai Wah Wu_, Oct 13 2023 %e A062855 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). %o A062855 (Python) %o A062855 from itertools import takewhile %o A062855 from sympy import divisors %o A062855 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 %Y A062855 Cf. A027424, A062851, A062854, A062856, A062857, A062858, A062859. %K A062855 nonn %O A062855 1,3 %A A062855 Ron A. Lalonde (ronronronlalonde(AT)hotmail.com), Jun 25 2001