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 A351690 #19 May 09 2022 08:34:50 %S A351690 1,3,14,52,42,310,0,684,584,1092,0,4788,0,7320,0,0,3276,31314,0,32004, %T A351690 0,0,0 %N A351690 a(n) is the number of n-subsets of [0..p-1] whose n*(n-1) differences are congruent to 1..p-1 (mod p), where p=n*(n-1)+1. %H A351690 Leonard E. Dickson, <a href="https://doi.org/10.2307/2968498">Problem 142</a>, The American Mathematical Monthly, Vol. 14, No. 5 (May, 1907), pp. 107-108. %H A351690 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PerfectDifferenceSet.html">Perfect Difference Set</a> %F A351690 a(n) = 2*(n*(n-1)+1)*A058241(n) for n >= 3. - _Pontus von Brömssen_, May 09 2022 %o A351690 (PARI) isok(n, v) = my(p=n*(n-1)+1); setbinop((x, y)->lift(Mod(x-y, p)), v, v) == [0..p-1]; %o A351690 a(n) = my(nb=0); forsubset([n^2-n+1, n], s, my(ds = apply(x->x-1, Vec(s))); if (isok(n, ds), nb++)); nb; %Y A351690 Cf. A058241, A353077. %K A351690 nonn,more %O A351690 1,2 %A A351690 _Michel Marcus_, May 05 2022 %E A351690 Name edited by _Pontus von Brömssen_, May 07 2022 %E A351690 a(1)-a(2) and a(8)-a(23) (based on data for A058241) from _Pontus von Brömssen_, May 09 2022