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 A141100 #9 Feb 20 2025 20:05:43
%S A141100 0,0,0,0,0,0,0,0,1,0,0,1,0,0,2,0,1,2,0,1,3,1,1,3,2,1,4,1,2,5,1,3,5,1,
%T A141100 4,5,3,3,6,3,3,7,3,3,9,3,4,7,4,6,9,5,5,8,6,6,10,5,5,12,4,6,12,5,9,11,
%U A141100 7,7,11,9,9,13,8,8,16,7,11,14,8,11,14,9,9,17,13,10,16,11,11,19,11,12,18,10
%N A141100 Number of unordered pairs of odd composite numbers that sum to 2n.
%C A141100 See A141099 for pairs of odd nonprime numbers. We have a(n) > 0 except for the 14 values of 2n given in A118081.
%H A141100 T. D. Noe, <a href="/A141100/b141100.txt">Table of n, a(n) for n=1..1000</a>
%F A141100 a(n) = 1 - floor(n/2) + Sum_{i=3..n} c(i) * c(2n-i), n>1, where c = A005171. - _Wesley Ivan Hurt_, Dec 27 2013
%e A141100 a(18)=2 because 36 = 9+27 = 15+21.
%t A141100 Table[cnt=0; Do[If[ !PrimeQ[i] && !PrimeQ[2n-i], cnt++ ], {i,3,n,2}]; cnt, {n,100}]
%Y A141100 Cf. A005171, A118081, A141095, A141097, A141099.
%K A141100 nonn
%O A141100 1,15
%A A141100 _T. D. Noe_, Jun 02 2008, Jun 05 2008