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 A261929 #15 Sep 19 2015 13:20:04 %S A261929 0,1,3,8,10,18,21,36,45,55,55,96,78,112,135,160,136,216,171,280,273, %T A261929 286,253,408,350,403,432,560,406,630,465,656,693,697,805,1008,666,874, %U A261929 975,1180,820,1260,903,1408,1485,1288,1081,1728,1323,1675,1683,1976,1378,2025,2035,2352,2109,2059,1711,2880,1830,2356 %N A261929 a(n) is the number of different pairs (p,q) mod n not of the form (x*y,x+y) mod n for any (x,y). %F A261929 a(n) = n^2 - A261928(n). %e A261929 a(2) = 1 because only the pair (1,1) mod 2 doesn't exist as result from any (x*y,x+y) mod 2. %Y A261929 Cf. A261928 (number of pairs that have such a form). %K A261929 nonn %O A261929 1,3 %A A261929 _Thomas Kerscher_, Sep 06 2015