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 A342138 #14 Mar 02 2021 05:58:39 %S A342138 1,0,3,2,5,8,7,10,13,16,15,18,21,24,27,26,29,32,35,38,41,40,43,46,49, %T A342138 52,55,58,57,60,63,66,69,72,75,78,77,80,83,86,89,92,95,98,101,100,103, %U A342138 106,109,112,115,118,121,124,127,126,129,132,135,138,141,144,147,150,153,156 %N A342138 Array T(n,k) = (n+k)*(3*n+3*k-5)/2 + (3*k+1), read by ascending antidiagonals. %C A342138 This is an instance of a storing function on N^2 (injective) with density 1/3. %H A342138 John S. Lew and Arnold L. Rosenberg, <a href="https://doi.org/10.1016/0022-314X(78)90035-5">Polynomial indexing of integer lattice-points I. General concepts and quadratic polynomials</a>, Journal of Number Theory, 10(2):215-243, 1978. See Corollary 5.2 p. 211. %e A342138 Array begins: %e A342138 1 3 8 16 27 ... %e A342138 0 5 13 24 38 ... %e A342138 2 10 21 35 52 ... %e A342138 7 18 32 49 69 ... %e A342138 15 29 46 66 89 ... %e A342138 ... %o A342138 (PARI) T(n,k) = (n+k)*(3*n+3*k-5)/2 + (3*k+1); %o A342138 matrix(8, 8, n, k, T(n-1, k-1)) %Y A342138 Cf. A005449 (first column), A104249 (first row), A140090 (second row), A201279 (diagonal). %K A342138 nonn,tabl %O A342138 0,3 %A A342138 _Michel Marcus_, Mar 01 2021