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 A178751 #43 Aug 19 2025 18:03:26 %S A178751 2,3,4,6,8,12,15,16,20,24,30,32,40,48,51,60,64,68,80,96,102,120,128, %T A178751 136,160,192,204,240,255,256,272,320,340,384,408,480,510,512,544,640, %U A178751 680,768,771,816,960,1020,1024,1028,1088,1280,1360,1536,1542,1632,1920,2040 %N A178751 Numbers k such that in Z/kZ the equation x^y + 1 = 0 has only the trivial solutions with x == -1 (mod k). %C A178751 It appears that odd terms 3, 15, 51, 255, 771, 3855, 13107, 65535, ... are given by A038192. - _Michel Marcus_, Aug 08 2013 %C A178751 This is the complement of A126949 in the numbers k > 1. (But it could be argued that the sequence should start with k = 1 as initial term.) It appears that for any a(j) in the sequence, 2*a(j) is also in the sequence. The primitive terms (not of the form a(j) = 2*a(m), m < j) are 2, 3, 15, 20, 51, 68, 255, 340, 771, 1028, .... (see A274003). - _M. F. Hasler_, Jun 06 2016 %H A178751 Arnaud Vernier and Charles R Greathouse IV, <a href="/A178751/b178751.txt">Table of n, a(n) for n = 1..189</a> (first 78 terms from Vernier) %e A178751 In Z/3Z, the only solution to the equation x^y + 1 = 0 is x = 2 and y = 1. Whereas in Z/5Z, the equation has at least one nontrivial solution: 2^2 + 1 = 0. %o A178751 (PARI) is(n)=for(x=2,n-2,if(gcd(x,n)>1,next);my(t=Mod(x,n));while(abs(centerlift(t))>1,t*=x);if(t==-1,return(0)));n>1 \\ _Charles R Greathouse IV_, Aug 08 2013 %Y A178751 Cf. A038192, A126949, A274003. %K A178751 nonn %O A178751 1,1 %A A178751 _Arnaud Vernier_, Jun 09 2010, Jun 10 2010