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 A039975 #18 Jul 08 2025 22:41:43 %S A039975 1,2,0,1,0,1,0,2,0,1,0,0,0,0,0,0,0,1,0,2,0,1,0,1,0,2,0,1,0,0,0,0,0,0, %T A039975 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,2,0,1,0,1,0,2,0,1,0,0,0,0, %U A039975 0,0,0,1,0,2,0,1,0,1,0,2,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 %N A039975 An example of a d-perfect sequence: a(n) = A006318(n-1) mod 3. %H A039975 Antti Karttunen, <a href="/A039975/b039975.txt">Table of n, a(n) for n = 1..11000</a> %H A039975 D. Kohel, S. Ling and C. Xing, <a href="http://www.maths.usyd.edu.au/u/kohel/doc/perfect.ps">Explicit Sequence Expansions</a>, in Sequences and their Applications, C. Ding, T. Helleseth, and H. Niederreiter, eds., Proceedings of SETA'98 (Singapore, 1998), 308-317, 1999. DOI: 10.1007/978-1-4471-0551-0_23 %F A039975 a(n) = A006318(n-1) mod 3. - _Christian G. Bower_, Jun 12 2005 %o A039975 (PARI) %o A039975 A006318(n) = if( n<1, 1, sum( k=0, n, 2^k * binomial( n, k) * binomial( n, k-1)) / n); %o A039975 A039975(n) = (A006318(n-1) % 3); \\ _Antti Karttunen_, Feb 13 2019 %Y A039975 Cf. A006318. %Y A039975 Cf. also A039969. %K A039975 nonn %O A039975 1,2 %A A039975 _N. J. A. Sloane_ %E A039975 More terms from _Christian G. Bower_, Jun 12 2005 %E A039975 Bower's formula added to the name by _Antti Karttunen_, Feb 13 2019