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 A079260 #25 Jul 14 2015 17:09:33
%S A079260 0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,
%T A079260 0,0,1,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,
%U A079260 0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,1,0,0,0,0
%N A079260 Characteristic function of primes of form 4n+1 (1 if n is prime of form 4n+1, 0 otherwise).
%C A079260 Let M(n) denote the n X n matrix m(i,j)=0 if n divides ij-1, m(i,j) = 1 otherwise then det(M(n))=-1 if and only if n =2 or if n is prime ==1 (mod 4).
%C A079260 a(A002144(n)) = 1; a(A137409(n)) = 0. [From _Reinhard Zumkeller_, Oct 11 2008]
%C A079260 a(n) * A151763(n) = a(n).
%H A079260 Reinhard Zumkeller, <a href="/A079260/b079260.txt">Table of n, a(n) for n = 1..10000</a>
%H A079260 <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>
%t A079260 Table[If[PrimeQ[n]&&IntegerQ[(n-1)/4],1,0],{n,120}] (* _Harvey P. Dale_, Jul 14 2015 *)
%o A079260 (PARI) { a(n)=if(n%4==1,isprime(n)) }; vector(100,n,a(n))
%o A079260 (Haskell)
%o A079260 a079260 n = fromEnum $ n `mod` 4 == 1 && a010051 n == 1
%o A079260 -- _Reinhard Zumkeller_, Oct 06 2011
%Y A079260 Cf. A002144, A079261.
%Y A079260 Cf. A066339 (partial sums).
%K A079260 nonn
%O A079260 1,1
%A A079260 _Benoit Cloitre_, Feb 04 2003