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 A055494 #27 Jul 15 2025 08:57:13
%S A055494 2,3,4,6,7,9,13,15,16,18,21,22,25,28,34,39,42,51,55,58,60,63,67,70,72,
%T A055494 76,78,79,81,90,91,100,102,106,111,112,118,120,132,139,142,144,148,
%U A055494 151,154,156,162,163,165,168,169,174,177,189,190,193,195,204,207,210,216
%N A055494 Numbers k such that k^2 - k + 1 is prime.
%C A055494 Also nonnegative integers such that a(n) + w is an Eisenstein prime, where w is the primitive cube root of unity. - _Frank M Jackson_, Jul 15 2025
%D A055494 M. Cerasoli, F. Eugeni and M. Protasi, Elementi di Matematica Discreta, Bologna 1988.
%D A055494 D. E. Knuth, "The Art of Computer Programming," Addison-Wesley, Reading, MA, Volume II, page 378.
%D A055494 Emanuele Munarini and Norma Zagaglia Salvi, Matematica Discreta,UTET, CittaStudiEdizioni, Milano 1997.
%H A055494 Vincenzo Librandi, <a href="/A055494/b055494.txt">Table of n, a(n) for n = 1..1000</a>
%H A055494 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/EisensteinPrime.html">Eisenstein Prime.</a>
%t A055494 Select[Range[300], PrimeQ[#^2 - # + 1] &] (* _Vincenzo Librandi_, Sep 28 2012 *)
%t A055494 lst = {}; Do[If[ResourceFunction["EisensteinIntegers"][n + w, w, "PrimeQ"],AppendTo[lst, n]], {n, 1, 300}]; lst (* _Frank M Jackson_, Jul 15 2025 *)
%o A055494 (Magma) [n: n in [1..300] |IsPrime(n^2 - n + 1)]; // _Vincenzo Librandi_, Sep 28 2012
%o A055494 (PARI) is(n)=isprime(n^2-n+1) \\ _Charles R Greathouse IV_, Feb 16 2017
%Y A055494 Equals A002384(n)+1.
%Y A055494 A002383 gives the primes.
%K A055494 nonn,easy
%O A055494 1,1
%A A055494 _Robert G. Wilson v_, Jul 05 2000
%E A055494 More terms from _David Wasserman_, Sep 15 2005