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 A002784 M0401 N0154 #19 Oct 20 2023 21:12:44 %S A002784 1,1,1,2,3,1,1,4,5,1,3,1,3,1,1,8,15,3,7,4,5,2,3,3,6,2,3,2,3,1,1,16,19, %T A002784 7,10,5,15,4,5,7,15,3,7,4,5,2,3,5,13,3,5,4,7,1,3,3,5,2,3,1,3,1,1,32, %U A002784 47,11,31,14,21,6,15,11,31,7,9,7,12,3,7,12,21,7,15,4,11,4,5,7,15,2,7,4,5 %N A002784 A problem in parity. %D A002784 H. Gupta, On a problem in parity, Indian J. Math., 11 (1969), 157-163. MR0260659 %D A002784 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). %D A002784 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A002784 H. Gupta, <a href="/A002783/a002783_1.pdf">On a problem in parity</a>, Indian J. Math., 11 (1969), 157-163. [Annotated scanned copy] %o A002784 (PARI) a(n)=if(n<1,0,sum(k=1,n,if(gcd(n,k) == 1,((n+k-1)!/(n!*k!))%2))) /* _Michael Somos_, Jul 19 2002 */ %Y A002784 Cf. A050169, A073166. %K A002784 nonn %O A002784 1,4 %A A002784 _N. J. A. Sloane_ %E A002784 More terms from _Michael Somos_, Jul 19 2002