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 A292411 #28 Feb 14 2025 19:08:14
%S A292411 1,4,2,3,10,13,5,6,22,8,28,31,11,12,40,15,46,17,18,55,20,21,67,73,76,
%T A292411 26,27,82,85,32,33,103,35,112,38,118,41,42,130,45,136,48,145,148,50,
%U A292411 53,56,57,172,175,60,181,63,193,66,202,68,208,211,71,220,77,78,235,238,83,253,87,262
%N A292411 a(n) = ((prime(n) - 1)/2)^2 modulo prime(n).
%C A292411 Also the square of (prime(n) - 1)/2 + 1 modulo prime(n).
%F A292411 a(n) = 4^(-1) mod prime(n). - _R. J. Cintra_, Jan 25 2025
%e A292411 The fourth prime is 7; ((7 - 1)/2)^2 = 3^2 = 9 = 2 mod 7. Hence a(4) = 2.
%e A292411 The fifth prime is 11; ((11 - 1)/2)^2 = 5^2 = 25 = 3 mod 11. Hence a(5) = 3.
%t A292411 Table[PowerMod[(Prime[n] - 1)/2, 2, Prime[n]], {n, 2, 70}]
%o A292411 (PARI) a(n) = lift(Mod((prime(n)-1)/2, prime(n))^2); \\ _Michel Marcus_, Sep 19 2017
%o A292411 (Python)
%o A292411 from sympy import prime
%o A292411 def A292411(n): return pow((p:=prime(n))-1>>1,2,p) # _Chai Wah Wu_, Feb 14 2025
%Y A292411 Cf. A005097.
%K A292411 nonn,easy
%O A292411 2,2
%A A292411 _Alonso del Arte_, Sep 16 2017